Physics157Updated 18 Sept 202613 pages

Essential Physics Keywords

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Welcome to your essential guide to GCSE Physics keywords! This summary covers the crucial terminology you'll need to master for your AQA GCSE Physics exams. Understanding these key terms will help you answer exam questions accurately and build confidence in your physics knowledge.

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Energy and Electricity Fundamentals

Physics is all about understanding how energy transforms and transfers. Waste energy is energy that isn't usefully used for the purpose of a system, while work done refers to energy transferred when a force acts over a distance. The watt measures power, equal to one joule of work per second.

In electricity, alternating potential difference creates an oscillating current flow, while direct potential difference flows in one direction only. Current (measured in amperes) is the rate of flow of electrical charge through a circuit. Components like diodes only allow current to flow in one direction, acting as electrical one-way valves.

Electric fields surround all charged objects, with field lines showing the direction a positive charge would move if placed in that field. When two opposite charges are brought near each other, they experience attraction, while like charges experience repulsion.

Remember this: All circuit components connected in series share the same current, while components in parallel share the same potential difference.

Safety features in electrical systems include the earth wire (green and yellow striped) that prevents appliances becoming live, and insulation around cables that prevents electrocution and aids identification.

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Electrical Components and Power Systems

Understanding how electrical components function is crucial for circuit analysis. The neutral wire (blue) completes the circuit in a mains power supply, while the live wire (brown) carries alternating current from the supply. Together with the earth wire, they form a safe electrical system.

Resistance measures opposition to current flow and is measured in ohms. Different components have unique resistance properties - thermistors increase resistance as temperature decreases, while light dependent resistors (LDRs) increase resistance as light levels decrease. An ohmic conductor has current directly proportional to potential difference at constant temperature.

When connecting resistors, remember that resistors in series add up $R = R₁ + R₂$ , while resistors in parallel follow the rule 1/R = 1/R₁ + 1/R₂. The total resistance of parallel resistors is always less than the lowest individual resistor value.

Quick tip: You can identify static charge by the attraction or repulsion effects it creates - it's caused by electrons moving from one surface to another through friction.

The National Grid distributes electricity using step-up transformers to increase voltage for transmission (reducing energy losses) and step-down transformers to deliver safe voltage levels to consumers. UK mains electricity supplies 230V at 50Hz.

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Particle Model of Matter

Matter exists in different states, and understanding the energy involved in state changes is key to this topic. The internal energy of a system is the total kinetic and potential energy of all its particles. When substances change state, they require energy known as latent heat without changing temperature.

State changes include melting (solid to liquid), freezing (liquid to solid), evaporation (liquid to gas), and condensation (gas to liquid). Some substances can undergo sublimation, changing directly from solid to gas. All these are physical changes because they can be reversed to restore original properties.

The specific heat capacity tells you how much energy is needed to raise 1kg of a substance by 1°C. Similarly, specific latent heat of fusion is the energy needed to change 1kg from solid to liquid, while specific latent heat of vaporisation is the energy needed to change 1kg from liquid to gas.

Exam tip: For gas particles, temperature is directly proportional to the average kinetic energy of molecules - higher temperature means faster-moving particles!

Density (mass per unit volume) and pressure (force per unit area, measured in pascals) are important physical properties. When calculating energy transfers, use the equation: change in thermal energy = mass × specific heat capacity × temperature change.

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Atomic Structure and Radiation

The atom has evolved from the simple Plum Pudding Model to the more sophisticated Bohr Model, which places electrons in specific energy levels orbiting the nucleus. The nucleus contains protons (positive) and neutrons (neutral), while electrons (negative) orbit in shells.

Every element has a unique atomic number (number of protons), while the mass number represents the total protons and neutrons. Isotopes have the same number of protons but different numbers of neutrons. When atoms gain or lose electrons, they become ions with positive or negative charge.

Radioactive decay occurs when unstable nuclei emit radiation to become more stable. The three main types of radiation are alpha particles (2 protons, 2 neutrons), beta particles (high-speed electrons), and gamma rays (electromagnetic waves). A Geiger-Muller tube measures the count-rate of radioactivity in becquerels.

Remember: Half-life is the time taken for half the unstable nuclei to decay or for the count rate to halve - it's unique to each isotope!

Nuclear fission involves splitting large unstable nuclei to release energy, while nuclear fusion joins small nuclei together. In fission reactions, neutrons can trigger a chain reaction that releases more neutrons and energy. This is the basis of nuclear power generation and nuclear explosions. Everyone is exposed to low levels of background radiation from natural sources like rocks and cosmic rays.

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Forces and Motion

Forces change an object's motion, shape, or both. Acceleration is the rate of change of velocity and can be calculated from velocity-time graphs. Understanding the difference between distance (how far something moves) and displacement (how far in a specific direction) is crucial.

When forces act on moving objects, they cause changes in momentum (mass × velocity). According to the principle of conservation of momentum, the total momentum before an interaction equals the total momentum after. This helps predict outcomes of collisions and explosions.

Objects can undergo elastic deformation (returning to original shape) or plastic deformation (permanent change) when forces are applied. The elastic limit is the maximum force that can be applied before permanent deformation occurs. Elastic potential energy is stored in stretched or compressed springs.

Physics in action: The Earth's atmosphere gets less dense with increasing altitude, which affects the pressure and forces experienced by objects moving through it!

When driving, your total stopping distance is the sum of thinking distance (affected by reaction time, drugs, alcohol) and braking distance (affected by road conditions, vehicle condition). Safe driving means understanding these factors and maintaining appropriate distances.

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Forces and Their Effects

An object's behavior depends on the forces acting upon it. The resultant force is the single force that replaces all individual forces with the same effect. If this is zero, the object is in equilibrium with no acceleration.

Newton's First Law states that objects continue in their state of rest or uniform motion unless acted upon by an external force. This resistance to change is called inertia, and is related to an object's inertial mass - the ratio of force to acceleration. According to Newton's Second Law, acceleration is directly proportional to force and inversely proportional to mass $F=ma$ .

Forces come in pairs - Newton's Third Law tells us that when objects interact, they exert equal and opposite forces on each other. Forces can be contact forces (requiring physical touching) or non-contact forces (acting at a distance).

Try this: Next time you're in a swimming pool, notice the upthrust keeping you afloat - it's because pressure increases with depth, creating more force on the bottom of an object than the top!

When an object is placed in a fluid (liquid or gas), it experiences pressure that increases with depth. An object will float when the upthrust equals its weight, and sink when the upthrust is less than its weight. The turning effect of a force is called a moment, calculated as force × perpendicular distance from the pivot. For an object to be stationary, the sum of clockwise and anticlockwise moments (the resultant moment) must be zero.

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Wave Properties and Behavior

Waves transfer energy without transferring matter. Key wave properties include amplitude (maximum displacement), wavelength (distance between equivalent points), frequency (waves per second, in hertz), and period (time for one complete wave). The wave speed equals frequency × wavelength.

Waves can be transverse (oscillations perpendicular to direction of travel, like light) or longitudinal (oscillations parallel to direction of travel, like sound). When waves meet boundaries, they can undergo reflection, where the angle of incidence equals the angle of reflection. Rough surfaces cause diffuse reflection (scattering), while smooth surfaces produce specular reflection (mirror-like).

An object's color depends on which wavelengths it absorbs or reflects. An object appears black if it absorbs all wavelengths, and white if it reflects all wavelengths. Colour filters work by absorbing certain wavelengths and transmitting others.

Sound science: The human ear can detect sound waves between 20Hz and 20kHz, but some animals can hear ultrasound waves above 20kHz. We use these for medical imaging and detecting objects underwater through echo sounding!

The Earth's structure can be studied using seismic waves produced by earthquakes. P-waves (primary) are longitudinal and can travel through solids and liquids, while S-waves (secondary) are transverse and cannot travel through liquids, helping scientists identify the Earth's liquid outer core.

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Electromagnetic Waves and Optics

Electromagnetic waves are transverse waves that form a continuous spectrum of different frequencies, all traveling at the same speed in a vacuum. The spectrum includes radio waves, microwaves, infrared, visible light, ultraviolet, X-rays, and gamma rays.

All objects emit and absorb infrared radiation based on their temperature - hotter objects emit more. A perfect black body would absorb all radiation falling on it without reflecting any. At constant temperature, an object absorbs energy at the same rate it emits it.

Visible light is the only part of the electromagnetic spectrum we can see. It's crucial for communications through fiber optics. Ultraviolet is used in energy-efficient lamps, while microwaves are used for cooking and satellite communications. Radio waves transmit television and radio signals.

Watch out! X-rays and gamma rays are forms of ionising radiation that can damage cells and DNA, potentially causing cancer. However, they're invaluable for medical imaging when used safely.

Lenses form images through refraction. A convex lens brings parallel rays to a focus at the principal focus, with the distance from the lens center to this point being the focal length. The image formed can be real or virtual, and its magnification is the ratio of image height to object height.

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Wave Applications and Phenomena

Waves are incredibly useful in modern technology and medicine. Ultrasound waves (above 20kHz) are used in ultrasound scanning to create images of internal body structures. The scanner transmits waves that reflect at tissue boundaries, and the time taken for reflections to return helps build detailed images.

Sound waves are longitudinal waves transmitted by vibrating particles in a medium. In solids, these vibrations pass efficiently from particle to particle. We can use sound for echo sounding to detect objects underwater and measure ocean depths by analyzing the time taken for sound to bounce back.

The reflection of waves follows a key rule: the angle of incidence always equals the angle of reflection. This principle applies to light, sound, and water waves. Understanding reflection helps explain how mirrors, echoes, and many optical devices work.

Did you know? The period of a wave (time for one complete cycle) is the inverse of its frequency. So a wave with frequency 50Hz has a period of 0.02 seconds!

The exposure of humans to electromagnetic radiation is measured as radiation dose, which indicates potential harm. Different types of radiation and different body tissues have varying sensitivity levels. This is particularly important in medical contexts like X-rays, where benefits must outweigh risks.

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Magnetism and Electromagnetism

Magnetism is all about invisible forces and fields. Magnetic fields exist around permanent magnets and can be represented by magnetic field lines showing direction and strength. These fields have magnetic poles (north and south) where forces are strongest. Unlike poles attract while like poles repel each other.

When a current flows through a wire, it creates a magnetic field around it - the basis of electromagnets. A solenoid (coil of wire) creates a strong, uniform magnetic field that can be enhanced by adding an iron core. Magnetic materials like iron, steel, cobalt, and nickel can become induced magnets when placed in a magnetic field.

The motor effect occurs when a current-carrying wire in a magnetic field experiences a force. Fleming's Left-Hand Rule helps determine the direction of this force: first finger points in magnetic field direction, second finger shows current direction, and thumb indicates the resulting force direction.

Making the connection: Electric motors, speakers, and headphones all work using the motor effect - they convert electrical energy into movement!

The generator effect is the reverse of the motor effect - when a conductor moves through a magnetic field, a potential difference is induced. This is how electricity generators work. Alternators produce alternating current, while dynamos produce direct current. Microphones convert sound waves into electrical signals using this principle. Transformers use electromagnetic induction to change voltage levels, with step-up transformers increasing voltage and step-down transformers decreasing it.

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Essential Physics Keywords

Energy and Electricity Fundamentals

Electrical Components and Power Systems

Particle Model of Matter

Atomic Structure and Radiation

Forces and Motion

Forces and Their Effects

Wave Properties and Behavior

Electromagnetic Waves and Optics

Wave Applications and Phenomena

Magnetism and Electromagnetism

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