cambridge igcse physics (3rd edition) by tom duncan and heather kennett.pdf

# Measurements and motion This topic explores the fundamental concepts of measurement in physics and the description of motion. ### 1.1 Measurements Measurements are essential for quantifying physical phenomena. #### 1.1.1 Units and powers of ten * **Basic quantities:** Three fundamental quantities in physics are length, mass, and time [21](#page=21). * **Prefixes:** Prefixes are used with base units to denote multiples or submultiples of ten. Common prefixes include [21](#page=21): * kilo (k): $10^3$ [21](#page=21). * centi (c): $10^{-2}$ [21](#page=21). * milli (m): $10^{-3}$ [21](#page=21). * micro ($\mu$): $10^{-6}$ [21](#page=21). * nano (n): $10^{-9}$ [21](#page=21). * **Powers of ten:** Numbers can be expressed using powers of ten, also known as standard notation [21](#page=21). > **Tip:** Understanding powers of ten is crucial for working with very large or very small numbers commonly encountered in physics, such as distances to stars or sizes of atoms [9](#page=9). #### 1.1.2 Length, area, and volume * **Length:** The basic unit of length is the meter (m) [21](#page=21). * **Area:** Area is the measure of a two-dimensional surface. * For a circle with radius $r$, the area is $A = \pi r^2$ [17](#page=17). * For a rectangle with length $l$ and breadth $b$, the area is $A = l \times b$. * **Volume:** Volume is the amount of space occupied by an object. * The SI unit of volume is the cubic meter ($m^3$), though the cubic centimeter ($cm^3$) is often used for convenience [17](#page=17). * Note that $1 m^3 = 1,000,000 cm^3 = 10^6 cm^3$ [17](#page=17). * For a regularly shaped object like a rectangular block, volume is calculated as length $\times$ breadth $\times$ height [17](#page=17). * The volume of a sphere with radius $r$ is $V = \frac{4}{3}\pi r^3$ [17](#page=17). * The volume of a cylinder with radius $r$ and height $h$ is $V = \pi r^2 h$ [17](#page=17). * Liquid volumes can be measured using measuring cylinders or burettes [17](#page=17). * Liquid volumes are also expressed in liters (l), where $1 \text{ litre} = 1000 \text{ cm}^3 = 1 \text{ dm}^3$. One milliliter (1 ml) is equal to $1 \text{ cm}^3$ [17](#page=17). * When reading a meniscus in a measuring cylinder or burette, the eye must be level with the bottom of the curved surface, except for mercury where the top is read [17](#page=17). #### 1.1.3 Mass * **Definition:** Mass is the measure of the amount of matter in an object [17](#page=17). * **Unit:** The SI unit of mass is the kilogram (kg) [17](#page=17). * **Gram:** The gram (g) is one-thousandth of a kilogram ($1 \text{ kg} = 1000 \text{ g}$) [17](#page=17). * **Measurement:** Mass is measured using various types of balances [17](#page=17). * **Inertia:** Mass is also a measure of inertia, which is an object's opposition to changes in its state of motion. A larger mass means greater inertia [43](#page=43). > **Tip:** Distinguish carefully between mass and weight, as they are distinct concepts with different units in science, even though the term "weighing" is used to find mass [17](#page=17). #### 1.1.4 Time * **Unit:** The basic unit of time is the second (s) [21](#page=21). * **Measurement:** Time is measured using clocks and timing devices, which can be analogue or digital [21](#page=21). * **Timers:** Tickertape timers can be used to record intervals of time by producing a series of dots on a tape. Each dot represents a specific time interval, often called a "tentick" [24](#page=24). * **Photogate timers:** These devices record the time taken for an object with an "interrupt card" to pass through the gate, allowing for velocity calculations [24](#page=24). * **Datalogging:** Motion sensors connected to dataloggers and computers can record distance and velocity data over time, generating graphs [24](#page=24). #### 1.1.5 Significant figures * **Definition:** Significant figures are the digits in a number that carry meaning contributing to its precision, including a final uncertain digit [21](#page=21). * **Appropriate number:** Results of measurements should be given to an appropriate number of significant figures to reflect the precision of the measuring instrument and method [21](#page=21). > **Tip:** When comparing measurements, consider the difference in precision. For example, the difference between 3.4 and 3.42 is due to the precision of the measurement [21](#page=21). #### 1.1.6 Precision measuring instruments * **Vernier calipers:** Used for measuring lengths with higher precision than a ruler [21](#page=21). * **Micrometer screw gauge:** Used for making very precise measurements, typically of small dimensions [21](#page=21). #### 1.1.7 Errors in measurement * **Systematic errors:** These are errors that consistently affect all measurements in the same way, leading to a bias. They can be introduced through faulty instruments or incorrect experimental procedures [21](#page=21). * **Minimizing errors:** Using precise measuring instruments and careful techniques helps to minimize errors [21](#page=21). ### 1.2 Motion Motion describes how an object changes its position over time. #### 1.2.1 Speed, velocity, and acceleration * **Speed:** The rate at which an object covers distance. * **Velocity:** The rate of change of displacement, meaning it includes both speed and direction [27](#page=27). * Uniform velocity means covering equal distances in equal times, resulting in a straight line on a distance-time graph [27](#page=27). * Non-uniform velocity means the speed or direction is changing, resulting in a curved or varying slope on a distance-time graph [27](#page=27). * **Acceleration:** The rate at which velocity changes [27](#page=27). * Uniform acceleration means the velocity changes by the same amount in equal time intervals [27](#page=27). * The acceleration ($a$) of a body can be calculated as the change in velocity ($\Delta v$) divided by the time taken ($\Delta t$): $a = \frac{\Delta v}{\Delta t}$ [27](#page=27). #### 1.2.2 Analyzing motion with graphs * **Distance–time graphs:** * The slope (gradient) of a distance-time graph represents the velocity of the body [27](#page=27). * A steeper slope indicates a higher velocity [27](#page=27). * For a changing velocity, the slope of the tangent at any point on the graph represents the instantaneous velocity [27](#page=27). * **Velocity–time graphs:** (Not explicitly detailed in the provided pages but implied by the context of analyzing motion with datalogging). The slope of a velocity-time graph represents acceleration, and the area under the graph represents displacement [24](#page=24). #### 1.2.3 Equations of motion for uniform acceleration For a body moving with uniform acceleration ($a$), initial velocity ($u$), final velocity ($v$), displacement ($s$), and time ($t$), the following equations apply: 1. **First equation:** Relates final velocity, initial velocity, acceleration, and time. $$v = u + at$$ [27](#page=27). 2. **Second equation:** Relates displacement, initial velocity, final velocity, and time. The average velocity for uniform acceleration is $\frac{u+v}{2}$ [27](#page=27). $$s = \frac{(u+v)}{2} t$$ [27](#page=27). 3. **Third equation:** Derived from the first two, relates final velocity, initial velocity, acceleration, and displacement. $$v^2 = u^2 + 2as$$ (This equation is not directly presented but is derivable from the first two and is a standard equation of motion). > **Tip:** Remember that initial and final velocities ($u$ and $v$) in these equations refer to the start and end of the time interval being considered, not necessarily the absolute start or end of the motion [27](#page=27). #### 1.2.4 Motion of falling bodies * **In a vacuum:** All objects fall at the same rate, irrespective of their mass, due to gravity [30](#page=30). * **In air:** Air resistance affects the motion of falling objects. Lighter objects are more significantly affected by air resistance relative to their weight than denser objects [30](#page=30). * **Acceleration of free fall ($g$):** Near the Earth's surface, objects experience a constant acceleration due to gravity, approximately $9.8 \text{ m/s}^2$. This value is often approximated as $10 \text{ m/s}^2$ for calculations. The weight of an object is given by $W = mg$ [47](#page=47). #### 1.2.5 Projectiles Projectile motion involves objects moving under the influence of gravity after being launched [30](#page=30). #### 1.2.6 Momentum * **Definition:** Momentum ($p$) is the product of an object's mass ($m$) and its velocity ($v$) [60](#page=60). $$p = mv$$ * **Units:** Momentum is measured in kilogram meters per second (kg m/s) or newton seconds (N s) [60](#page=60). * **Conservation of momentum:** In the absence of external forces, the total momentum of a system remains constant during collisions and explosions. This means the total momentum before an event equals the total momentum after the event [60](#page=60). > **Example:** A 2 kg mass moving at 10 m/s has a momentum of 20 kg m/s. This is the same as a 5 kg mass moving at 4 m/s [60](#page=60). --- # Thermal physics and properties of waves This topic delves into the fundamental principles of thermal physics, exploring the behavior of matter at a microscopic level and its response to heat, alongside the characteristics and behavior of various wave phenomena. ### 2.1 Thermal physics Thermal physics examines the relationship between heat, work, and energy, and how these interact with matter. #### 2.1.1 Kinetic molecular model of matter The kinetic molecular theory describes matter as being composed of tiny particles (molecules or atoms) that are in constant motion [85](#page=85). * **Solids:** In solids, molecules are closely packed and are held together by strong attractive and repulsive forces. They vibrate about fixed positions [85](#page=85). * **Liquids:** Molecules in liquids are still close together but have more freedom to move around compared to solids. The forces between them are weaker, allowing them to flow [88](#page=88). * **Gases:** In gases, molecules are far apart and exert negligibly small forces on each other, except during collisions. They move rapidly and occupy all available space [88](#page=88). ##### 2.1.1.1 Brownian motion Brownian motion is the random movement of microscopic particles suspended in a fluid (liquid or gas). This motion is caused by collisions with the fast-moving molecules of the fluid. A smoke particle, for example, moves haphazardly due to imbalances in the number and force of collisions from air molecules striking it from different directions [85](#page=85). > **Tip:** Brownian motion provides experimental evidence for the existence and motion of molecules. #### 2.1.2 Gas laws Gas laws describe the relationships between pressure, volume, temperature, and the amount of a gas. * **Boyle's Law:** For a fixed mass of gas at a constant temperature, the pressure is inversely proportional to its volume. This can be expressed as $pV = \text{constant}$, or $p_1V_1 = p_2V_2$ [91](#page=91). * If pressure doubles, volume halves, and vice versa [91](#page=91). * A graph of pressure against volume is a curve, while a graph of pressure against $1/V$ is a straight line through the origin [91](#page=91). #### 2.1.3 Thermal properties Thermal properties relate to how substances interact with heat. * **Expansion:** Most substances expand when heated and contract when cooled. This is due to the increased kinetic energy of molecules, leading to larger average separations [97](#page=97). * The increase in length of a heated metal bar depends on its original length and the temperature rise [97](#page=97). * **Bimetallic strip:** A bimetallic strip consists of two metals with different thermal expansivities joined together. When heated, the strip bends because one metal expands more than the other. This principle is used in thermostats [97](#page=97). * **Specific heat capacity:** This is the amount of heat energy required to raise the temperature of 1 kilogram of a substance by 1 degree Celsius (or Kelvin). The formula is : $$ \text{Specific heat capacity} = \frac{\text{heat received}}{\text{mass} \times \text{temperature rise}} $$ $$ c = \frac{Q}{m \Delta T} $$ The unit is Joules per kilogram per degree Celsius (J/(kg °C)) . * **Importance of water's high specific heat capacity:** Water has a high specific heat capacity (approximately 4200 J/(kg °C)). This means it takes a lot of energy to change its temperature, and it releases a lot of energy when cooling. This moderates coastal climates, as sea temperatures change more slowly than land temperatures. Water is also used in cooling systems and central heating radiators . * **Latent heat:** This is the energy absorbed or released during a change of state (e.g., melting, boiling) at a constant temperature . * **Latent heat of fusion:** The energy required to change a substance from solid to liquid at its melting point. This energy increases the potential energy of the molecules as they overcome intermolecular forces . * **Latent heat of vaporisation:** The energy required to change a substance from liquid to gas at its boiling point. This energy is used to overcome intermolecular forces and also to do work against the atmosphere during expansion . * The formula is $Q = m \times l_v$, where $Q$ is the energy, $m$ is the mass, and $l_v$ is the specific latent heat of vaporisation . * **Evaporation and boiling:** * **Evaporation:** The process by which molecules escape from the surface of a liquid into the gaseous phase. It occurs at all temperatures and is faster at higher temperatures, with larger surface areas, and in drier air . * **Boiling:** Occurs when the vapor pressure of a liquid equals the surrounding atmospheric pressure, leading to the formation of bubbles within the liquid . #### 2.1.4 Temperature measurement While not explicitly detailed with specific instruments in the provided text, temperature is a fundamental property measured to quantify the thermal state of a system and is used in calculations involving specific heat capacity and gas laws. #### 2.1.5 Thermal processes (Heat transfer) Heat can be transferred through conduction, convection, and radiation. * **Conduction:** The transfer of heat through direct contact between particles. It is significant in solids . * **Convection:** The transfer of heat through the movement of fluids (liquids or gases). Warmer, less dense fluid rises, while cooler, denser fluid sinks, creating convection currents . * **Examples:** Coastal breezes (land heats and cools faster than sea) and thermals (rising columns of hot air used by gliders) are natural convection phenomena . * **Radiation:** The transfer of heat through electromagnetic waves. It does not require a medium and can travel through a vacuum . * **Greenhouse effect:** Glass traps long-wavelength infrared radiation emitted by objects heated by the Sun, increasing the temperature inside the greenhouse. Atmospheric gases like carbon dioxide and methane act similarly, trapping heat and influencing global climate . * **Absorbers and emitters:** Surfaces that are good absorbers of radiation are also good emitters when hot . * **Vacuum flask:** Designed to minimize heat transfer by conduction, convection (vacuum between walls), and radiation (silvered surfaces) . * **Rate of cooling:** The rate at which an object cools is proportional to the ratio of its surface area to its volume (A/V). Objects with a larger A/V ratio cool more quickly . ### 2.2 Properties of waves Waves are disturbances that transfer energy through a medium or space. #### 2.2.1 General wave properties * **Wavefront:** A surface joining points that are in the same phase of oscillation. * **Huygens' construction:** A method to determine the position of a wavefront at a later time. Each point on a wavefront acts as a source of secondary spherical wavelets, and the new wavefront is the tangent surface to these wavelets. This principle explains reflection, refraction, and diffraction . * **Diffraction:** The spreading of waves as they pass through a gap or around an obstacle . #### 2.2.2 Light Light is a form of electromagnetic radiation that exhibits wave-like properties. * **Sources of light:** * **Luminous sources:** Objects that emit their own light, such as the Sun, lamps, and candles . * **Non-luminous objects:** Objects that reflect light from a luminous source, such as a page, a person, or the Moon . * **Laser:** A source that emits a narrow, very bright beam of coherent light due to excited atoms acting together . * **Rays and beams:** * **Ray:** The path along which light travels, represented by a straight line with an arrow . * **Beam:** A stream of light shown by multiple rays. Beams can be parallel, diverging, or converging. Light travels in straight lines in a uniform medium . * **Shadows:** Regions where light is blocked by an opaque object . * **Speed of light:** Light travels at a finite speed . * **Reflection of light:** The bouncing back of light when it strikes a surface . * **Law of reflection:** 1. The angle of incidence equals the angle of reflection ($i=r$) . 2. The incident ray, the reflected ray, and the normal all lie in the same plane . * **Normal:** A line perpendicular to the reflecting surface at the point of incidence . * **Regular reflection:** Occurs from smooth surfaces, producing a clear image . * **Diffuse reflection:** Occurs from rough surfaces, scattering light in many directions . * **Multiple images in mirrors:** Mirrors silvered at the back can form multiple images due to internal reflections, which can blur the main image. Front-silvered mirrors avoid this but are easily damaged . * **Totally reflecting prisms:** Used in periscopes and binoculars to redirect light through 90° or 180° using total internal reflection, overcoming the limitations of mirrors . * **Refraction of light:** The bending of light as it passes from one medium to another . * Light bends **towards** the normal when entering an optically denser medium (e.g., air to glass) . * Light bends **away** from the normal when entering an optically less dense medium (e.g., glass to air) . * Light traveling along the normal direction is not refracted . * **Refractive index (n):** A measure of how much light bends in a medium. It is the ratio of the speed of light in a vacuum to the speed of light in the medium. It is also related to the critical angle ($c$) by $n = \frac{1}{\sin c}$. For example, if $n = 3/2$, then $\sin c = 2/3$, and $c$ must be 42° . * **Critical angle:** The angle of incidence in the denser medium for which the angle of refraction in the less dense medium is 90°. If the angle of incidence exceeds the critical angle, total internal reflection occurs . * **Dispersion:** The splitting of white light into its constituent colours when passing through a prism, due to different colours (wavelengths) refracting at slightly different angles . #### 2.2.3 Sound Sound is a form of energy that travels as waves, typically through a medium like air. While the provided text mentions sound in the context of the electromagnetic spectrum, specific properties of sound waves (like speed, frequency, amplitude) are not detailed in the specified pages. #### 2.2.4 The electromagnetic spectrum The electromagnetic spectrum is the range of all types of electromagnetic radiation, ordered by frequency or wavelength. This includes radio waves, microwaves, infrared radiation, visible light, ultraviolet radiation, X-rays, and gamma rays. Different parts of the spectrum have different properties and applications. Radiation from very hot bodies is mostly light and short-wavelength infrared, while less hot objects emit long-wavelength infrared . --- # Electricity and magnetism and atomic physics This section explores the fundamental principles of electricity and magnetism, their applications in electronic systems and power generation, and the basic structure and properties of atoms including radioactivity . ### 3.1 Electricity and magnetism fundamentals #### 3.1.1 Magnetic fields Magnetic fields are regions around magnets or current-carrying conductors where magnetic forces are exerted. These fields are represented by lines of force, where the direction at any point indicates the force on a North pole . * **Properties of magnets:** Magnets attract magnetic materials like iron and steel . * **Soft and hard magnetic materials:** These differ in their ability to retain magnetism. * **Mapping magnetic fields:** Fields can be mapped using plotting compasses or iron filings . * **Neutral points:** These are locations where the magnetic field from one source is cancelled by the field from another . #### 3.1.2 Static electricity Static electricity involves electric charges that are stationary. It can be generated through friction, leading to the transfer of electrons . * **Uses of static electricity:** * **Flue-ash precipitation:** Used in power stations to remove dust and ash from chimneys by giving particles a charge and then attracting them to oppositely charged plates . * **Photocopiers:** Utilize a charged drum to create a toner pattern that is then transferred to paper . * **Inkjet printers:** Charge tiny ink drops electrostatically to control their deflection and precise placement on paper . * **Computers:** Require anti-static conditions to prevent electrostatic damage . #### 3.1.3 Electric current An electric current is the flow of electric charge. In metals, this flow is primarily of electrons from the negative to the positive terminal of a battery within a closed circuit . * **Effects of electric current:** Currents produce thermal, chemical, and magnetic effects . * **Measurement of current:** Current is measured in amperes (A) using an ammeter connected in series with the circuit . * **Circuit symbols:** Standard symbols exist for wires, cells, switches, ammeters, and lamps . * **Series and parallel circuits:** * In series circuits, the current is the same throughout . * In parallel circuits, the total current from the source is the sum of the currents in each branch . * **Direct current (d.c.) and alternating current (a.c.):** * D.C. flows in one direction, typically from batteries . * A.C. periodically reverses direction, with its frequency measured in cycles per second (Hertz) . * **Charge and current relation:** The quantity of charge ($Q$) is related to current ($I$) and time ($t$) by $Q = It$ . #### 3.1.4 Potential difference Potential difference (p.d.), or voltage, is the energy transferred per unit charge. It is measured in volts (V) using a voltmeter connected in parallel across the component or circuit section of interest . * **Voltages in series circuits:** The total voltage across components in series is the sum of the individual voltages across each component . * **Voltages in parallel circuits:** The voltage across components connected in parallel is equal for all components . * **Potential divider:** A series circuit of resistors can divide a voltage. The voltage across a resistor in a series combination is given by $V_{R1} = V_{supply} \times \frac{R1}{R1 + R2}$ and $V_{R2} = V_{supply} \times \frac{R2}{R1 + R2}$ . #### 3.1.5 Resistance Resistance is a measure of how much a material opposes the flow of electric current. It is measured in ohms ($\Omega$) . * **Factors affecting resistance:** Resistance depends on the material's resistivity ($\rho$), length ($l$), and cross-sectional area ($A$), given by $R = \rho \frac{l}{A}$ . * **Ohm's Law:** Relates voltage ($V$), current ($I$), and resistance ($R$) as $V = IR$ . #### 3.1.6 Electric power Electric power is the rate at which electrical energy is transferred or converted. It is measured in watts (W) . * **Power formulas:** Power ($P$) can be calculated using $P = VI$, $P = I^2R$, and $P = \frac{V^2}{R}$ . * **Joulemeter:** An instrument that directly measures electrical energy transferred in joules . * **Household circuits:** Typically operate in parallel at a mains p.d. of 230 V in the UK. Switches and fuses are always placed in the live wire for safety . #### 3.1.7 Electronic systems Electronic systems use components like transistors, diodes, and integrated circuits to process information . * **Input transducers:** Convert physical quantities into electrical signals (e.g., Light-dependent resistors (LDRs) whose resistance changes with light intensity, and thermistors whose resistance changes with temperature) . * **Output transducers:** Convert electrical signals into physical quantities (e.g., relays, speakers) . * **Transistors:** Can function as switches or amplifiers. They are crucial in modern electronics due to their small size, low power consumption, and speed . * **Diodes:** Allow current to flow in one direction only . #### 3.1.8 Generators Generators convert mechanical energy into electrical energy using the principle of electromagnetic induction . * **Alternators:** Produce alternating current (a.c.) and are commonly used in power stations and cars . * **Dynamos:** Produce direct current (d.c.). * **Bicycle generators:** Utilize a rotating magnet to induce voltage in a stationary coil . #### 3.1.9 Transformers Transformers are devices that change the voltage of alternating current (a.c.) using electromagnetic induction between coils wound around a common iron core . * **Turns ratio:** The ratio of voltages in a transformer is equal to the ratio of the number of turns on the secondary ($N_s$) and primary ($N_p$) coils: $\frac{V_s}{V_p} = \frac{N_s}{N_p}$ . * **Step-up and step-down transformers:** Step-up transformers increase voltage (and decrease current), while step-down transformers decrease voltage (and increase current) . * **Power transmission:** Transformers are essential for the efficient transmission of electrical power over long distances by stepping up voltage to reduce current and thus minimize energy loss due to resistance . * **Eddy currents:** These are induced currents in the transformer core that cause heating and are reduced by using laminated cores . #### 3.1.10 Electromagnets Electromagnets are temporary magnets created by passing an electric current through a coil of wire . * **Oersted's discovery:** Demonstrated that an electric current produces a magnetic field . * **Field patterns:** The magnetic field pattern depends on the shape of the conductor (straight wire, coil, solenoid) . * **Right-hand screw rule:** Used to determine the direction of the magnetic field around a current-carrying wire . * **Applications:** Electromagnets are used in electric bells, relays, and circuit breakers . #### 3.1.11 Electric motors Electric motors convert electrical energy into mechanical energy, typically using the interaction between magnetic fields and current-carrying conductors . * **Working principle:** A current-carrying coil placed in a magnetic field experiences a torque that causes it to rotate . * **Components:** Motors typically consist of a rotor (rotating part, often a coil) and a stator (stationary part, often magnets) . * **Commutator:** In d.c. motors, a commutator reverses the direction of current in the coil at appropriate times to maintain continuous rotation . #### 3.1.12 Electric meters Various meters are used to measure electrical quantities. * **Ammeters:** Measure electric current and are connected in series. They have low resistance . * **Voltmeters:** Measure potential difference and are connected in parallel. They have high resistance . * **Joulemeter:** Measures electrical energy directly in joules . * **Cathode Ray Oscilloscope (CRO):** A versatile instrument that can display voltage waveforms over time, measure voltages, and analyze electrical signals . #### 3.1.13 Electrons Electrons are fundamental negatively charged particles that are the primary charge carriers in electric currents within metals. Their movement is responsible for many electrical phenomena . ### 3.2 Atomic physics This area covers the structure of atoms, radioactivity, and nuclear energy . #### 3.2.1 Atomic structure Atoms consist of a central nucleus containing protons and neutrons, surrounded by orbiting electrons . * **Nuclear models:** Various models have been developed to describe the atom's structure . * **Particle properties:** Protons, neutrons, and electrons have specific masses and charges that define their behavior within an atom . #### 3.2.2 Radioactivity Radioactivity is the spontaneous emission of radiation from the nucleus of an unstable atom . * **Radioactive decay:** Unstable nuclei transform into more stable ones by emitting alpha particles ($\alpha$), beta particles ($\beta$), or gamma rays ($\gamma$) . * **Nuclear energy:** The energy released from nuclear reactions, such as fission and fusion, has significant applications . #### 3.2.3 Nuclear energy Nuclear energy is derived from nuclear reactions, most commonly nuclear fission, where the nucleus of a heavy atom splits into lighter nuclei, releasing a large amount of energy. This energy is harnessed in nuclear power stations to generate electricity . --- ## Common mistakes to avoid - Review all topics thoroughly before exams - Pay attention to formulas and key definitions - Practice with examples provided in each section - Don't memorize without understanding the underlying concepts

| Term | Definition | |---|---| | SI units | The International System of Units, a standardized system of measurement used in science, including units like the meter for length, kilogram for mass, and second for time. | | Powers of ten shorthand | A method of writing very large or very small numbers concisely by using powers of 10, such as $4 \times 10^3$ for 4000. | | Length | A measure of distance. The SI unit for length is the meter (m). | | Significant figures | The number of digits in a measurement that are considered reliable, indicating the precision of the measurement. | | Area | The measure of the extent of a two-dimensional surface. The SI unit is the square meter ($m^2$). | | Volume | The amount of three-dimensional space occupied by a substance or object. The SI unit is the cubic meter ($m^3$). | | Mass | A measure of the amount of matter in an object. The SI unit is the kilogram (kg). | | Time | The measure of the duration of events or the interval between them. The SI unit for time is the second (s). | | Systematic errors | Errors in measurement that consistently affect the result in the same way, often due to faulty equipment or experimental design. | | Vernier scales and micrometers | Precision measuring instruments used to measure lengths with greater accuracy than a standard ruler, typically to two or three decimal places of a centimeter. | | Speed | The rate at which an object covers distance. It is calculated as distance divided by time. | | Velocity | The rate of change of displacement, indicating both speed and direction of motion. | | Acceleration | The rate at which velocity changes, either in magnitude or direction. | | Timers | Devices used to measure intervals of time, such as stopwatches, tickertape timers, and photogate timers. | | Velocity–time graphs | Graphs that plot velocity on the y-axis against time on the x-axis, used to analyze motion. The slope represents acceleration, and the area under the graph represents distance traveled. | | Distance–time graphs | Graphs that plot distance on the y-axis against time on the x-axis. The slope of the graph represents velocity. | | Equations for uniform acceleration | A set of equations ($v = u + at$, $s = ut + \frac{1}{2}at^2$, $v^2 = u^2 + 2as$) used to solve problems involving motion with constant acceleration. | | Falling bodies | Objects that are falling freely under the influence of gravity, typically with uniform acceleration if air resistance is negligible. | | Acceleration of free fall (g) | The constant acceleration experienced by an object falling freely under gravity, approximately $9.8 \, m/s^2$ near the Earth's surface. | | Projectiles | Objects launched into the air or space, whose motion can be analyzed by considering their horizontal and vertical components independently. | | Density | The mass of a substance per unit volume, calculated as $ \rho = \frac{m}{V} $. | | Pressure | The force acting perpendicularly on a unit area of a surface. The SI unit is the pascal (Pa). | | Liquid pressure | The pressure exerted by a liquid, which increases with depth and density, calculated as $ p = h\rho g $. | | Force | A push or pull that can cause an object to accelerate, change shape, or change its state of motion. Measured in Newtons (N). | | Weight | The force of gravity acting on an object's mass, calculated as $ W = mg $. | | The Newton | The SI unit of force. | | Hooke’s Law | The extension of an elastic object is directly proportional to the stretching force applied, provided the elastic limit is not exceeded ($ F = kx $). | | Resultant force | The single force that has the same effect as all the individual forces acting on an object; found by vector addition. | | Friction | A force that opposes motion or attempted motion between surfaces in contact. | | Newton’s first law of motion | An object at rest stays at rest, and an object in motion stays in motion with the same speed and in the same direction unless acted upon by an unbalanced force. | | Inertia | The tendency of an object to resist changes in its state of motion; directly related to mass. | | Newton’s second law of motion | The acceleration of an object is directly proportional to the net force acting on it and inversely proportional to its mass ($ F = ma $). | | Gravitational field strength | The force per unit mass experienced by an object in a gravitational field. It is numerically equal to the acceleration due to gravity ($ g $). | | Newton’s third law of motion | For every action, there is an equal and opposite reaction. Forces occur in pairs acting on different objects. | | Terminal velocity | The constant speed reached by a falling object when the force of air resistance equals its weight, resulting in zero net force. | | Circular motion | The motion of an object along a circular path. | | Centripetal force | The force acting towards the center of a circular path that causes an object to move in a circle. It is calculated as $ F = \frac{mv^2}{r} $. | | Satellites | Objects that orbit a celestial body, with their orbital motion maintained by gravity providing the centripetal force. | | Moments and levers | The turning effect of a force about a pivot point, calculated as force multiplied by the perpendicular distance from the pivot ($ \text{Moment} = \text{Force} \times \text{distance} $). Levers are devices that use a pivot to multiply force. | | Conditions for equilibrium | For an object to be in equilibrium, the vector sum of all forces acting on it must be zero, and the sum of all moments about any point must also be zero. | | Centre of mass | The point where the entire mass of an object can be considered to be concentrated. | | Toppling | An object topples when the vertical line through its centre of mass falls outside its base of support. | | Stability | The tendency of an object to return to its original position after being disturbed. It is increased by lowering the centre of mass and widening the base. | | Neutral equilibrium | A state where an object remains in its new position when displaced. | | Momentum | The product of an object's mass and its velocity ($ p = mv $). It is a vector quantity. | | Conservation of momentum | The total momentum of a system remains constant in the absence of external forces. | | Impulse | The product of a force and the time over which it acts ($ \text{Impulse} = F \times t $), equal to the change in momentum. | | Energy transfer | The movement of energy from one form to another or from one object to another. | | Forms of energy | Energy exists in various forms, including chemical, potential, kinetic, electrical, heat, light, sound, and nuclear energy. | | Work | Done when a force causes displacement. Calculated as force multiplied by the distance moved in the direction of the force ($ W = Fd $). Measured in joules (J). | | Power | The rate at which work is done or energy is transferred. Calculated as work divided by time ($ P = \frac{W}{t} $). Measured in watts (W). | | Energy conservation | Energy cannot be created or destroyed, only transformed from one form to another. | | Efficiency | The ratio of useful energy output to total energy input, usually expressed as a percentage ($ \text{Efficiency} = \frac{\text{Useful Output}}{\text{Total Input}} \times 100\% $). | | Energy of food | The amount of energy released when food is metabolized, measured in joules per kilogram. | | Combustion of fuels | The process of burning fuels to release energy, typically as heat and light. | | Kinetic energy (k.e.) | The energy possessed by an object due to its motion. Calculated as $ E_k = \frac{1}{2}mv^2 $. | | Potential energy (p.e.) | Stored energy due to an object's position or condition. Gravitational potential energy is $ E_p = mgh $. | | Elastic collisions | Collisions where kinetic energy is conserved. | | Inelastic collisions | Collisions where kinetic energy is not conserved, usually converted into other forms like heat or sound. | | Braking distance | The distance a vehicle travels while its brakes are applied to bring it to a stop; directly proportional to the square of the speed. | | Crumple zones | Designed areas in vehicles that deform during a collision, absorbing energy and increasing the impact time to reduce injury. | | Energy sources | Materials or phenomena that can be used to produce useful energy. They are classified as renewable or non-renewable. | | Non-renewable energy sources | Energy sources that are finite and cannot be replenished on a human timescale, such as fossil fuels and nuclear fuels. | | Renewable energy sources | Energy sources that are naturally replenished and generally non-polluting, such as solar, wind, wave, tidal, hydroelectric, geothermal, and biomass energy. | | Power stations | Facilities that generate electricity, often using various energy sources to produce steam that drives turbines connected to generators. | | Thermal power stations | Power stations that use heat (from fossil fuels or nuclear reactions) to produce steam to drive turbines. | | Hydroelectric power stations | Power stations that use the potential energy of falling water to drive turbines. | | Wind turbines | Devices that convert the kinetic energy of wind into electrical energy using generators. | | Solar energy | Energy derived from the Sun, harnessed through solar panels (electricity) or solar furnaces (heat). | | Geothermal energy | Heat energy from within the Earth, used for generating electricity or heating. | | Biomass | Organic matter from plants and animals used as an energy source, often converted into biofuels or biogas. | | Pressure | The force acting per unit area ($ p = F/A $). Measured in pascals (Pa). | | Liquid pressure | Pressure within a liquid, dependent on depth ($ h $), density ($ \rho $), and acceleration due to gravity ($ g $), given by $ p = h\rho g $. | | Hydraulic machines | Devices that use the properties of liquids (incompressibility and pressure transmission) to multiply force, such as hydraulic jacks and brakes. | | Manometers | Instruments used to measure pressure, often by comparing the pressure of a gas or liquid to atmospheric pressure using a column of liquid. | | Barometers | Instruments used to measure atmospheric pressure, typically using a column of mercury. | | Conduction | Heat transfer through a material without the bulk movement of the material itself, occurring through molecular collisions and electron movement in metals. | | Convection | Heat transfer through fluids (liquids or gases) by the movement of the fluid itself, driven by density differences. | | Radiation | Heat transfer through electromagnetic waves, which can occur through a vacuum. | | Vacuum flask | A container designed to minimize heat transfer by all three methods: conduction, convection, and radiation. | | Molecules | The tiny particles that make up matter, in continuous motion and exerting forces on each other. | | Kinetic theory of matter | A model that explains the states of matter (solid, liquid, gas) and their properties based on the motion and interactions of molecules. | | Solids | State of matter where molecules are closely packed and vibrate about fixed positions. | | Liquids | State of matter where molecules are close but can move past each other, taking the shape of their container but maintaining a definite volume. | | Gases | State of matter where molecules are far apart, move randomly at high speeds, and fill the entire volume of their container. | | Diffusion | The spreading of particles from an area of higher concentration to an area of lower concentration due to random molecular motion. | | Crystals | Solids with a regular, repeating arrangement of atoms or molecules, characterized by flat sides and straight edges. | | Brownian motion | The random, haphazard movement of microscopic particles suspended in a fluid, caused by collisions with the fluid's molecules. | | Gas laws | Relationships describing the behavior of gases concerning pressure, volume, and temperature (Boyle's Law, Charles's Law, Pressure Law, Combined Gas Law). | | Absolute zero | The theoretical lowest possible temperature (0 K or -273.15 °C) at which molecular motion ceases. | | Kelvin scale | An absolute temperature scale where absolute zero is 0 K. Temperature in Kelvin ($ T $) is related to Celsius ($ \theta $) by $ T = \theta + 273 $. | | Boyle's Law | For a fixed mass of gas at constant temperature, pressure is inversely proportional to volume ($ pV = \text{constant} $). | | Charles's Law | For a fixed mass of gas at constant pressure, volume is directly proportional to absolute temperature ($ V/T = \text{constant} $). | | Pressure Law | For a fixed mass of gas at constant volume, pressure is directly proportional to absolute temperature ($ p/T = \text{constant} $). | | Expansion | The increase in volume of a substance when heated. | | Linear expansivity ($ \alpha $) | The fractional increase in length of a material per degree Celsius rise in temperature. | | Bimetallic strip | A strip made of two metals with different thermal expansion coefficients, used in thermostats and fire alarms as a temperature-sensitive switch. | | Unusual expansion of water | Water expands when cooled from 4 °C to 0 °C, making ice less dense than water and causing it to float. | | Thermometers | Devices used to measure temperature, relying on physical properties that change with temperature. | | Fixed points | Standard temperatures used to calibrate thermometers, typically the melting point of ice (0 °C) and the boiling point of water (100 °C). | | Clinical thermometer | A special thermometer with a narrow range and constriction to accurately measure body temperature. | | Thermocouple thermometer | A thermometer that uses the voltage generated at the junction of two different metals to measure temperature. | | Resistance thermometer | A thermometer that measures temperature based on the change in electrical resistance of a material, such as platinum wire. | | Thermistors | Semiconductor devices whose resistance changes significantly with temperature, often decreasing as temperature increases. | | Heat | Thermal or internal energy of a body, related to the kinetic and potential energy of its molecules. Measured in joules (J). | | Temperature | A measure of the average kinetic energy of the molecules in a substance, indicating how hot or cold it is. Measured in degrees Celsius (°C) or Kelvin (K). | | Specific heat capacity ($ c $) | The amount of heat required to raise the temperature of 1 kg of a substance by 1 °C. Measured in J/(kg °C). | | Thermal capacity | The quantity of heat required to raise the temperature of a body by 1 °C. It is equal to mass × specific heat capacity. | | Heat equation | Relates heat transfer ($ Q $) to mass ($ m $), specific heat capacity ($ c $), and temperature change ($ \Delta\theta $): $ Q = mc\Delta\theta $. | | Latent heat | Energy absorbed or released during a change of state (e.g., melting, boiling) without a change in temperature. | | Specific latent heat of fusion ($ l_f $) | The heat required to change 1 kg of a substance from solid to liquid at its melting point. | | Specific latent heat of vaporisation ($ l_v $) | The heat required to change 1 kg of a substance from liquid to gas at its boiling point. | | Evaporation | The process where liquid molecules escape from the surface into the gaseous phase at any temperature, leading to cooling. | | Boiling | The process where liquid turns into gas with the formation of bubbles throughout the liquid at a specific temperature (boiling point). | | Condensation | The process where a gas changes into a liquid, releasing latent heat of vaporisation. | | Solidification | The process where a liquid changes into a solid, releasing latent heat of fusion. | | Liquefaction of gases | The process of converting a gas into a liquid, typically by cooling below its critical temperature and/or increasing pressure. | | Conduction | Heat transfer through a material by molecular collisions and electron movement, without bulk movement of the material. | | Convection | Heat transfer through fluids by the movement of the fluid itself, driven by density differences. | | Radiation | Heat transfer through electromagnetic waves, which can travel through a vacuum. | | Vacuum flask | A container designed to minimize heat transfer by conduction, convection, and radiation. | | Electromagnetic radiation | Waves that consist of oscillating electric and magnetic fields traveling at the speed of light, forming a continuous spectrum. | | Light waves | Electromagnetic radiation within the visible spectrum, responsible for sight and color perception. | | Infrared radiation (IR) | Electromagnetic radiation with longer wavelengths than visible light, detected as heat. | | Ultraviolet radiation (UV) | Electromagnetic radiation with shorter wavelengths than visible light, capable of causing fluorescence and skin damage. | | Radio waves | Electromagnetic waves with the longest wavelengths and lowest frequencies in the spectrum, used for communication. | | X-rays | Electromagnetic radiation with very short wavelengths, capable of penetrating matter and used in medical imaging. | | Gamma rays | Electromagnetic radiation of very short wavelength and high frequency, emitted from atomic nuclei, highly penetrating and ionising. | | Wavefronts | Lines or surfaces connecting points in a wave that are in the same phase. | | Rays | Lines drawn perpendicular to wavefronts, indicating the direction of wave travel. | | Wave equation ($ v = f\lambda $) | Relates the speed of a wave ($ v $) to its frequency ($ f $) and wavelength ($ \lambda $). | | Reflection | The bouncing of waves off a surface, where the angle of incidence equals the angle of reflection. | | Refraction | The bending of waves as they pass from one medium to another, caused by a change in wave speed. | | Diffraction | The spreading of waves as they pass through an opening or around an obstacle. | | Wave theory | A model explaining wave phenomena like reflection, refraction, and diffraction using Huygens' construction, where each point on a wavefront acts as a source of secondary wavelets. | | Interference | The phenomenon occurring when two or more waves overlap, resulting in a new wave pattern (e.g., constructive or destructive interference). | | Polarisation | An effect occurring only with transverse waves, describing the orientation of the oscillations relative to the direction of travel. | | Sound waves | Longitudinal waves produced by vibrations, which travel through a medium as compressions and rarefactions. | | Longitudinal waves | Waves in which the particles of the medium vibrate parallel to the direction of wave travel. | | Echoes | Sound waves reflected from a surface. | | Limits of audibility | The range of sound frequencies that humans can hear, typically from 20 Hz to 20 kHz. | | Musical notes | Sounds with regular vibrations, characterized by pitch (frequency), loudness (amplitude), and quality (overtones). | | Ultrasonics | Sound waves with frequencies above the human hearing range (> 20 kHz), used in medical imaging, sonar, and industrial applications. | | Seismic waves | Waves generated by earthquakes, including longitudinal (P-waves) and transverse (S-waves) types. | | Magnetic fields | The region around a magnet or current-carrying conductor where magnetic forces are exerted. Represented by lines of force. | | Properties of magnets | Magnets attract magnetic materials (iron, steel, nickel, cobalt), have poles (North and South), and exhibit magnetic fields. | | Magnetic poles | Regions of a magnet where magnetic forces are strongest, always existing in pairs (North and South). Like poles repel, unlike poles attract. | | Magnetisation | The process of making a magnetic material magnetic, often by exposing it to a magnetic field. | | Soft magnetic materials | Materials that are easily magnetized but also easily demagnetized, used in electromagnets. | | Hard magnetic materials | Materials that are harder to magnetize but retain their magnetism, used for permanent magnets. | | Field lines | Lines used to represent the direction and strength of a magnetic field; they point from North to South poles, and their density indicates field strength. | | Earth’s magnetic field | The magnetic field surrounding the Earth, produced by currents in its core, which influences compasses. | | Static electricity | The accumulation of electric charge on an object, typically an insulator, due to friction. | | Electric charge | A fundamental property of matter, existing in positive (+) and negative (-) forms. Like charges repel; unlike charges attract. | | Electrons | Negatively charged particles orbiting the nucleus of an atom; their movement constitutes electric current. | | Insulators | Materials that do not allow electric charge to flow easily. | | Conductors | Materials that allow electric charge to flow easily, typically due to free electrons. | | Electrostatic induction | The process by which a charged object influences the distribution of charge in a nearby conductor, causing separation of charges. | | van de Graaff generator | A device that produces high-voltage static electricity by transferring charge onto a rotating belt. | | Electric fields | The region around an electric charge where another charge experiences a force. Represented by field lines pointing from positive to negative charges. | | Electric current | The flow of electric charge. Measured in amperes (A). | | Ampere (A) | The SI unit of electric current, defined by the magnetic effect of current. | | Coulomb (C) | The SI unit of electric charge, equal to the charge passing a point when a current of 1 ampere flows for 1 second ($ 1 C = 1 A \cdot s $). | | Circuit diagrams | Schematic representations of electrical circuits using standard symbols for components like batteries, wires, switches, lamps, ammeters, and voltmeters. | | Series circuits | Circuits where components are connected end-to-end, providing only one path for current. The current is the same through all components. | | Parallel circuits | Circuits where components are connected side-by-side, providing multiple paths for current. The total current is the sum of currents in each branch, and the voltage across each branch is the same. | | Direct current (d.c.) | Electric current that flows in one direction only. | | Alternating current (a.c.) | Electric current that periodically reverses direction. | | Hertz (Hz) | The SI unit of frequency, representing one cycle per second. | | Potential difference (p.d.) | The work done per unit charge in moving charge between two points in a circuit. Also called voltage. Measured in volts (V). | | Volt (V) | The SI unit of potential difference and electromotive force. 1 volt equals 1 joule per coulomb ($ 1 V = 1 J/C $). | | Cells, batteries and e.m.f. | Cells convert chemical energy to electrical energy. Batteries are combinations of cells. Electromotive force (e.m.f.) is the maximum potential difference of a source when no current flows, representing energy transferred per unit charge. | | Voltmeters | Instruments used to measure potential difference, connected in parallel across the component. They have high resistance. | | Ammeters | Instruments used to measure electric current, connected in series within the circuit. They have low resistance. | | Resistance | The opposition to the flow of electric current in a conductor. Measured in ohms ($ \Omega $). | | Ohm ($ \Omega $) | The SI unit of resistance. 1 ohm is the resistance when 1 ampere of current flows with a potential difference of 1 volt across it. | | Resistors | Components designed to have a specific resistance value. | | Ohm's Law | For an ohmic conductor, the current is directly proportional to the potential difference ($ V = IR $). | | Ohmic (linear) conductors | Conductors for which the I-V graph is a straight line through the origin, meaning resistance is constant regardless of voltage or current. | | Non-ohmic conductors | Conductors for which the I-V graph is not a straight line, indicating that resistance changes with voltage, current, or temperature (e.g., filament lamps, diodes, thermistors). | | Potential divider | A circuit arrangement using resistors in series to provide a variable output voltage from a fixed voltage supply. | | Resistor colour code | A system of colored bands on resistors that indicates their resistance value and tolerance. | | Resistivity ($ \rho $) | A material's intrinsic resistance to electrical current, independent of its shape or size. Calculated using $ R = \frac{\rho l}{A} $. | | Capacitors | Electronic components that store electric charge and energy. | | Capacitance (C) | A measure of a capacitor's ability to store charge, defined as the charge stored per unit potential difference ($ C = Q/V $). Measured in farads (F). | | Farad (F) | The SI unit of capacitance. | | Electrolytic capacitors | Capacitors with a very thin dielectric layer, offering high capacitance values but requiring correct polarity during connection. | | Charging and discharging a capacitor | The process of storing charge on a capacitor by connecting it to a voltage source, and releasing the stored charge by connecting it across a conductor or resistor. | | Electric power | The rate at which electrical energy is transferred or converted into other forms. Calculated as $ P = IV = I^2R = V^2/R $. Measured in watts (W). | | Kilowatt (kW) | A unit of power equal to 1000 watts. | | Kilowatt-hour (kWh) | A unit of electrical energy, equal to the energy consumed by a 1 kW appliance operating for 1 hour. | | Fuses | Safety devices containing a wire that melts and breaks the circuit if the current exceeds a safe limit, preventing overheating and fires. | | Earthing | A safety measure connecting the metal casing of an appliance to the ground to provide a low-resistance path for fault current, preventing electric shock. | | Circuit breakers | Automatic switches that interrupt a circuit when an overcurrent occurs, can be reset after a fault is cleared. | | Residual current devices (RCDs) | Safety devices that detect imbalances in current between live and neutral wires, interrupting the circuit to prevent electric shock, especially in damp conditions. | | Double insulation | An appliance design with two layers of insulation to protect users from electric shock, eliminating the need for an earth connection. | | Electronic systems | Systems comprising input sensors, processors, and output transducers that process electrical signals. | | Transducers | Devices that convert energy from one form to another, such as non-electrical to electrical (sensors) or electrical to non-electrical (output devices). | | Input transducers (sensors) | Devices that detect physical changes and convert them into electrical signals (e.g., LDRs, thermistors, microphones). | | Output transducers | Devices that convert electrical signals into other forms of energy (e.g., lamps, LEDs, loudspeakers, motors). | | Light-dependent resistor (LDR) | A semiconductor device whose resistance decreases as the intensity of light falling on it increases. | | Thermistors | Semiconductor devices whose resistance changes significantly with temperature, often decreasing as temperature rises. | | Relays | Electrically operated switches that use an electromagnet to control a second circuit, often with a higher current or voltage. | | Light-emitting diodes (LEDs) | Semiconductor devices that emit light when forward-biased; efficient and long-lasting indicators and light sources. | | Diodes | Semiconductor devices that allow current to flow in only one direction, used for rectification. | | Rectification | The process of converting alternating current (a.c.) to direct current (d.c.) using diodes. | | Transistors | Semiconductor devices with three terminals (base, collector, emitter) used as amplifiers or switches in electronic circuits. | | Transistor as a switch | A transistor can act as an electronically controlled switch, turning a larger collector current on or off based on a small base current or voltage. | | Digital electronics | Electronic systems that process information represented by discrete values (high/low voltage levels, 1s and 0s), used in computers and logic circuits. | | Analogue electronics | Electronic systems that process continuously varying signals. | | Logic gates | Electronic switching circuits that perform logical operations (AND, OR, NOT, NAND, NOR) based on input signals, forming the basis of digital electronics. | | Truth table | A table that shows the output of a logic gate for all possible combinations of input values. | | Logic levels | The two discrete voltage levels (high/1 and low/0) used in digital electronics. | | Generators | Devices that convert mechanical energy into electrical energy, utilizing electromagnetic induction. | | Electromagnetic induction | The production of an electromotive force (e.m.f.) or voltage in a conductor when it is exposed to a changing magnetic field or moves through a magnetic field. | | Faraday’s Law | The magnitude of the induced e.m.f. in any closed circuit is directly proportional to the rate of change of magnetic flux through the circuit. | | Lenz’s Law | The direction of an induced current is such that it opposes the change in magnetic field that produced it. | | Fleming’s right-hand rule (Dynamo rule) | A mnemonic to determine the direction of induced current in a conductor moving in a magnetic field: Field (first finger), Motion (thumb), Current (second finger). | | AC generator (alternator) | A device that produces alternating current by rotating a coil in a magnetic field, using slip rings to maintain continuous a.c. output. | | DC generator (dynamo) | A device that produces direct current by using a commutator to reverse the connections to the external circuit as the coil rotates, ensuring unidirectional current. | | Practical generators | Real-world generators, often using electromagnets for stronger fields and multiple coils for smoother output, found in power stations and vehicles. | | Transformers | Devices that change alternating voltages using electromagnetic induction between two coils wound on a common iron core. | | Mutual induction | The induction of an e.m.f. in a secondary coil due to a changing current in a nearby primary coil. | | Transformer equation ($ V_s/V_p = N_s/N_p $) | Relates the voltages and number of turns in the primary ($ p $) and secondary ($ s $) coils of an ideal transformer. | | Energy losses in a transformer | Occur due to resistance of windings (heat), eddy currents in the core, and leakage of magnetic flux. | | Eddy currents | Circulating currents induced within a conductor by a changing magnetic field, often causing heating. | | Transmission of electrical power | The process of transporting electrical energy over long distances, typically using high alternating voltages to minimize energy loss due to resistance in transmission lines. | | Electromagnets | Temporary magnets created by passing an electric current through a coil of wire, often wound around a soft iron core. Their strength depends on current, number of turns, and core material. | | Field due to a straight wire | Magnetic field lines form concentric circles around a current-carrying wire. The direction is given by the right-hand screw rule. | | Field due to a circular coil | Magnetic field lines are concentrated inside the coil, forming a pattern similar to a short bar magnet. | | Field due to a solenoid | Produces a uniform magnetic field inside and a dipole field outside, similar to a bar magnet. The direction is given by the right-hand grip rule. | | Magnetisation and demagnetisation | Processes of making materials magnetic or removing magnetism, often using solenoids. | | Electric bells | Devices that use an electromagnet to repeatedly strike a gong, creating a continuous ringing sound. | | Relays | Electrically operated switches using electromagnets to control a separate circuit. | | Reed switches | Switches operated by magnetic fields, often activated by a nearby magnet or an electromagnet in a coil. | | Circuit breakers | Safety devices that interrupt a circuit in case of overcurrent, often using electromagnets; they can be reset. | | Telephones | Devices that convert sound into electrical signals (microphone) and electrical signals back into sound (receiver), often using carbon microphones and electromagnets. | | Cathode rays | Beams of high-speed electrons emitted from a hot cathode in a vacuum tube. | | Thermionic emission | The emission of electrons from a heated surface, such as a filament in a vacuum tube. | | Deflection of an electron beam | Electron beams can be deflected by electric fields (towards positive charges) and magnetic fields (perpendicular to both velocity and field, following Fleming's left-hand rule). | | Cathode Ray Oscilloscope (CRO) | An electronic instrument that displays the waveform of electrical signals by deflecting an electron beam across a fluorescent screen. | | X-rays | High-energy electromagnetic radiation produced when high-speed electrons strike a target; penetrating and ionising, used in medical imaging and industry. | | Photoelectric effect | The emission of electrons from a metal surface when illuminated by electromagnetic radiation of sufficient frequency (photons), demonstrating the particle nature of light. | | Waves or particles? | Electromagnetic radiation exhibits both wave-like (interference, diffraction) and particle-like (photons, photoelectric effect) properties, indicating a dual nature. | | Radioactivity | The spontaneous emission of radiation from unstable atomic nuclei. | | Ionising effect of radiation | The ability of radiation (alpha, beta, gamma) to knock electrons off atoms, creating ions, which can discharge electroscopes and affect photographic film. | | Geiger–Müller (GM) tube | A device used to detect and measure ionizing radiation by counting electrical pulses produced when radiation passes through a gas-filled tube. | | Alpha particles ($ \alpha $) | Positively charged particles (helium nuclei) emitted during radioactive decay; highly ionizing but with short range. | | Beta particles ($ \beta $) | High-energy electrons ($ \beta^- $) or positrons ($ \beta^+ $) emitted during radioactive decay; less ionizing than alpha particles but more penetrating. | | Gamma rays ($ \gamma $) | Highly penetrating electromagnetic radiation emitted from atomic nuclei, not deflected by electric or magnetic fields. | | Particle tracks | Visible paths left by ionizing radiation in detection devices like cloud chambers or bubble chambers, indicating the type of radiation and its behavior in fields. | | Radioactive decay | The process by which unstable atomic nuclei transform into more stable ones by emitting radiation, occurring spontaneously and at a characteristic rate. | | Half-life | The average time taken for half of the radioactive atoms in a sample to decay. | | Activity | The rate at which radioactive decays occur in a sample, often measured in counts per second or minute. | | Random nature of decay | Radioactive decay is a random process; the exact time of decay for a specific atom cannot be predicted, only the probability of decay over a period. | | Uses of radioactivity | Radioisotopes are used in industry (thickness gauging, tracers), medicine (diagnostics, radiotherapy), archaeology (carbon dating), and sterilization. | | Dangers and safety | Exposure to ionizing radiation can damage cells and tissues. Safety precautions include distance, shielding (lead, concrete), limiting exposure time, and using monitoring devices (dose badges). | | Atomic structure | The arrangement of protons, neutrons, and electrons within an atom. | | Nuclear atom | A model of the atom proposed by Rutherford, consisting of a small, dense, positively charged nucleus surrounded by orbiting electrons. | | Nucleons | Protons and neutrons found in the nucleus of an atom. | | Isotopes | Atoms of the same element (same number of protons) but with different numbers of neutrons, thus different nucleon numbers. | | Nuclides | A specific type of atom defined by its number of protons and neutrons. Isotopes are nuclides with the same proton number but different nucleon numbers. | | Radioactive decay | The spontaneous transformation of unstable nuclei, involving the emission of alpha, beta, or gamma radiation. | | Nuclear stability | The stability of a nucleus depends on the balance between protons and neutrons. Nuclides near the 'stability line' are more stable. | | Models of the atom | Representations of atomic structure, such as the Rutherford-Bohr model (miniature solar system) and the Schrödinger model (electron clouds and energy levels). | | Nuclear energy | Energy released from nuclear reactions like fission (splitting of heavy nuclei) and fusion (joining of light nuclei), related to mass defect by $ E=mc^2 $. | | Fission | The splitting of a heavy atomic nucleus, typically uranium-235, into lighter nuclei, releasing energy and neutrons, which can sustain a chain reaction. | | Nuclear reactor | A device used to control nuclear fission reactions to produce energy, typically for electricity generation. | | Fusion | The process where light atomic nuclei combine to form heavier nuclei, releasing large amounts of energy, as occurs in stars like the Sun. |