WJEC GCSE Physics Revision
GCSE Physics · Wales
Revising for WJEC GCSE Physics? Below is every topic in the course, in specification order, with a short summary. Sign up free to get the full notes, quizzes, flashcards and exam questions for each one — filtered to the WJEC course so you only revise what's on your exam.
WJEC GCSE Physics topics
1 Electric circuits
Electric current is the rate of flow of charge, measured in Amperes (A). Voltage (or potential difference) is the energy transferred per unit charge, measured in Volts (V). It's the 'push' that makes current flow. Resistance is the opposition to current flow, measured in Ohms (Ω). A higher resistance means less current flows for a given voltage. These three are fundamentally linked by Ohm's Law.
2 Generating electricity
Electromagnetic induction is the process of generating an electromotive force (e.m.f.) or voltage across an electrical conductor in a changing magnetic field. This principle is fundamental to how most electricity is generated. When a conductor, like a coil of wire, moves through a magnetic field, or when the magnetic field through a stationary coil changes, a current is induced. The magnitude of the induced current depends on the strength of the magnetic field, the speed of movement, and the number of turns in the coil. This effect is described by Faraday's law of induction.
3 Making use of energy
Energy cannot be created or destroyed, only transferred from one store to another. Common energy stores include kinetic (moving objects), gravitational potential (objects in a gravitational field), elastic potential (stretched/compressed objects), chemical (stored in bonds), thermal (hot objects), and nuclear (in atomic nuclei). Energy can be transferred mechanically (by forces), electrically (by current), by heating (due to temperature difference), or by radiation (waves like light/sound). Understanding these transfers is key to analysing energy changes.
4 Domestic electricity
In the UK, mains electricity is an alternating current (AC) supply. This means the direction of the current continuously changes. The standard frequency is 50 Hz, meaning the current direction changes 50 times per second, and the voltage is 230 V. Alternating current is used for mains because it can be easily transformed to different voltages using transformers, which is efficient for transmission over long distances. Direct current (DC), found in batteries, flows in only one direction. Most domestic appliances are designed for AC.
5 Features of waves
A wave is a disturbance that transfers energy from one place to another without transferring matter. Waves can be mechanical (requiring a medium to travel, like sound) or electromagnetic (not requiring a medium, like light). All waves involve an oscillation or vibration. Understanding this fundamental concept is crucial before delving into specific wave types and their properties. Key examples include water waves, sound waves, and light waves.
6 Total internal reflection of waves
Total Internal Reflection (TIR) is an optical phenomenon where a light ray, travelling from a denser medium towards a less dense medium, is completely reflected back into the denser medium. This happens when the angle of incidence at the interface exceeds a specific value called the critical angle. Instead of refracting (bending away from the normal), the light bounces off the boundary entirely, just like it would off a mirror. This principle is crucial in many technologies.
7 Seismic waves
Seismic waves are waves of energy that travel through the Earth's layers, and are a result of sudden movement of rock within the Earth, such as an earthquake. They carry energy from the source of the disturbance outwards. Scientists study these waves using instruments called seismographs to understand the Earth's internal structure. There are several types, each with distinct properties. Understanding them is crucial for detecting earthquakes and exploring the Earth's interior.
8 Kinetic theory
The kinetic theory explains the properties of solids, liquids, and gases based on the movement of their particles. In **solids**, particles are tightly packed in a regular arrangement, vibrating about fixed positions. In **liquids**, particles are closely packed but randomly arranged, able to slide past each other. In **gases**, particles are widely spaced, randomly arranged, and move rapidly and randomly in all directions. The forces between particles are strongest in solids, weaker in liquids, and negligible in gases. Changing state involves changing the energy and arrangement of these particles.
9 Electromagnetism
When an electric current flows through a wire, it creates a magnetic field around the wire. For a straight wire, the field lines are concentric circles centred on the wire, their direction given by the right-hand grip rule. If the wire is coiled into a solenoid, the magnetic field inside becomes strong and uniform, similar to a bar magnet. The strength of this field depends on the current, the number of turns in the coil, and the core material. Increasing these factors strengthens the electromagnet.
10 Distance, speed and acceleration
Distance is a scalar quantity, meaning it only has magnitude. It's the total path length covered by an object. For example, if you walk 5m north and then 3m south, your total distance covered is 8m. Displacement, however, is a vector quantity, possessing both magnitude and direction. It's the straight-line distance from the starting point to the final point, including the direction. In the previous example, your displacement would be 2m North, assuming you started at a reference point.
11 Newton's laws
Newton's First Law, also known as the Law of Inertia, states that an object will remain at rest or continue to move at a constant velocity unless acted upon by a net (resultant) external force. This means if the forces acting on an object are balanced, its motion won't change. If it's stationary, it stays stationary; if it's moving, it keeps moving at the same speed in the same direction. This law highlights that force is needed to change an object's state of motion, not to maintain it.
12 Work and energy
In physics, **work is done** when a force causes an object to move through a distance in the direction of the force. It's a measure of the energy transferred. If you push a box across a floor, you are doing work on it. If you hold a heavy object but don't move it, no work is done *in the physics sense*, even though it might feel tiring. The unit for work done is the joule (J), which is also the unit for energy. Work done can be calculated using the formula: `Work Done (J) = Force (N) × Distance (m)`.
13 Further motion concepts
In physics, quantities are classified as either scalar or vector. A **scalar quantity** has only magnitude (size), such as distance (e.g., 5 km), speed (e.g., 20 m/s), mass (e.g., 3 kg), time, and energy. A **vector quantity** has both magnitude and direction, for example, displacement (e.g., 5 km East), velocity (e.g., 20 m/s North), force (e.g., 10 N downwards), and acceleration. Understanding this distinction is crucial for correctly solving problems involving motion.
14 Stars and planets
Our Solar System consists of the Sun, eight planets, dwarf planets, moons, asteroids, and comets. The planets orbit the Sun in elliptical paths, held in orbit by the Sun's gravitational force. Inner planets (Mercury, Venus, Earth, Mars) are rocky, while outer planets (Jupiter, Saturn, Uranus, Neptune) are gas giants. Understanding the relative sizes and distances of these components helps us grasp the vastness of space. Many smaller bodies also populate the asteroid belt and Kuiper belt.
15 The Universe
The prevailing scientific theory for the origin of the universe is the Big Bang. It postulates that the universe began from an extremely hot, dense point (singularity) approximately 13.8 billion years ago. Since then, the universe has been expanding and cooling, leading to the formation of fundamental particles, then atoms, and eventually stars, galaxies, and all the structures we observe today. Evidence for the Big Bang includes cosmic microwave background radiation and the red-shift of distant galaxies.
16 Types of radiation
Alpha radiation consists of two protons and two neutrons, identical to a helium nucleus (⁴₂He). It is the most ionising type of radiation but has the lowest penetrating power, stopped by a few centimetres of air or a sheet of paper. Alpha particles have a positive charge (+2e) and are deflected by electric and magnetic fields. They are emitted by large, unstable nuclei during alpha decay to become more stable. Though easily stopped externally, alpha emitters are very dangerous if ingested or inhaled, as they can cause significant internal tissue damage.
17 Half-life
Half-life is the time it takes for half of the radioactive nuclei in a sample to decay. It's a fundamental property of a particular radioactive isotope and doesn't change with temperature, pressure, or chemical state. For example, if a sample initially contains 1000 radioactive nuclei, after one half-life, 500 will remain. After two half-lives, 250 will remain, and so on. It's a random process for individual atoms, but predictable for large numbers of atoms. Half-life can range from fractions of a second to billions of years.
18 Nuclear decay and nuclear energy
Radioactive decay is the spontaneous and random process by which unstable atomic nuclei lose energy by emitting radiation. This process transforms the unstable 'parent' nucleus into a more stable 'daughter' nucleus. The emitted radiation can be alpha particles, beta particles, or gamma rays. This decay is not affected by external factors like temperature, pressure, or chemical bonding. Each radioactive isotope has a characteristic half-life, which is the time taken for half of the nuclei in a sample to decay.
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