# Physics Paper 1 Revision: Energy, Electricity, Particle Model of Matter & Atomic Structure

The Beyond Science Team explores Physics Paper 1 revision for GCSE Science, providing bite-sized revision for each topic on the AQA syllabus, including:

### Atomic Structure

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## Physics Paper 1 Revision: Energy

### Kinetic and Potential Energy Stores

When an object is lifted in a gravitational field it has a store of gravitational potential energy.

gravitational potential energy = mass × gravitational field strength × height

When an object falls, energy is transferred from the gravitational potential energy store to the kinetic energy store.

kinetic energy = ½ × mass × (speed)²

When an object is stretched or squashed, energy is transferred to its elastic potential energy store.

elastic potential energy = ½ × spring constant × (extension)²

### Energy Stores and Systems

Energy can be transferred in the following ways:

• Mechanically: when work is done by a force;
• Electrically: when a charge is moved through a potential difference;
• Heating: when energy is transferred from a hotter object to a colder object;
• Radiation: when energy is transferred as electromagnetic waves or as moving subatomic particles.

### Transferring Energy by Heating

Heating a material transfers the energy to its thermal energy stores and the temperature increases.

Kettle example:

Energy is transferred to the thermal energy store of the kettle. Energy is transferred by heating to the water’s thermal energy store. The temperature of the water will then increase.

Some materials need more energy to increase their temperature than others.

change in thermal energy = mass × specific heat capacity × temperature change

Specific heat energy is the amount of energy needed to raise the temperature of 1kg of a material by 1°C.

Heat can be transferred by conduction, convection or radiation:

• Conduction: when a solid is heated, the particles vibrate and collide more frequently, transferring energy in the process.
• Convection: when a liquid or gas is heated, the particles move faster. This causes the particles to spread further apart and take up a greater volume. This means the liquid or gas becomes less dense, so it rises above a cooler region. The denser, cool liquid or gas falls, creating a convection current.
• Radiation: heat can be transferred by infrared radiation, a type of electromagnetic radiation that involves waves. All objects emit some infrared radiation.

### Conservation of Energy

Energy can never be created or destroyed, just transferred from one form to another. Some energy is transferred usefully and some energy gets dissipated (transferred to the environment as wasted energy).

### Power

Power is the rate of energy transfer or the amount of work done in a given time.

power = energy transferred ÷ time

power = work done ÷ time

### Energy Transfer

Lubrication reduces the amount of friction. When an object moves, there are frictional forces acting. Some energy is lost to the environment.

Lubricants, such as oil, can be used to reduce the friction between the surfaces.

Insulation: reduces the amount of heat loss. In your home, you can prevent heat loss in a number of ways:

• thick walls;
• thermal insulation (loft insulation, cavity walls, double glazing).

### Efficiency

When energy is transferred, some energy is wasted. The less energy that is wasted during the transfer, the more efficient the transfer.

There are two equations to calculate efficiency:

• efficiency = useful output energy transfer ÷ total input energy transfer
• efficiency = useful power output ÷ total power input

Some energy is always lost. Nothing is 100% efficient…not even Beyond.

Non-renewable resource, e.g. coal, oil, gas – an energy resource which cannot be replenished in a lifetime and will eventually run out.

Renewable resource – an energy resource which can be replenished as it is used and will not run out.

## Physics Paper 1 Revision: Electricity

### Charge

Electric current is the flow of electric charge. It only flows when the circuit is complete.
The charge is the current flowing past a point in a given time. Charge is measured in coulombs (C).

### Calculating Charge

charge flow (C) = current (A) × time (s)

### Resistance

potential difference (V) = current (A) × resistance (Ω)

• Ohmic conductor: A component in which the resistance remains constant as the current changes, provided its temperature is the same.
• Filament lamp: A component that contains a thin coil of wire that heats up and therefore produces light when an electric current passes through it. As the current increases, so does the temperature. This causes the resistance to increase, making it harder for the current to flow.
• Diode: A non-ohmic conductor that allows current to flow in one direction only. It has a very high resistance in the reverse direction.

### Circuit Devices

LDR – Light Dependent Resistor

• An LDR is dependent on light intensity. In bright light the resistance is low. As the light intensity decreases, the resistance increases.
• Uses of LDRs: outdoor night lights, burglar detectors.

Thermistor

• A thermistor is a temperature-dependent resistor. If it is hot, then the resistance is low. As the temperature decreases, the resistance increases.
• Uses of thermistors: thermostats.

### Series and Parallel Circuits

Series Circuits – A circuit in which the current follows one path. If one of the components in the circuit is broken then all the components will stop working.

• Potential difference – The total potential difference of the power supply is shared between all the components.
• Current – The current is the same everywhere in a series circuit.
• Resistance – In a series circuit, total resistance of the circuit is the sum of the resistances of the individual components.

Parallel Circuits – A circuit in which the current divides into two or more paths before recombining to complete the circuit. If one component stops working, it will not affect the components on other branches.

• Potential difference – The potential difference is the same across each branch of a parallel circuit.
• Current – The total current is split between the different branches.
• Resistance – The total resistance of the circuit is reduced as the current can flow in multiple paths.

### Electricity in the Home

• Alternating current (ac) electric current in a circuit that repeatedly changes direction. The UK mains electricity is an ac supply with a potential difference of 230V and a frequency of 50Hz.
• Direct current (dc) – Electric current in a circuit that flows in one direction only. This type of current is supplied by batteries.
• Cables – most have three wires: live, neutral and earth. They are covered in plastic insulation for safety.
• Live wire – carries the alternating potential difference from the supply. It is coloured brown for easy identification. Touching the live wire can cause the current to flow through your body. This causes an electric shock.
• Neutral wire – completes the circuit. It is coloured blue for easy identification.
• Earth wire – stops the appliance from becoming live. It provides a path for electric current to flow from the case of the appliance to the ground if there is a fault. It is coloured with green and yellow stripes.

The amount of energy transferred by an appliance depends on how long the appliance is on for and its power.

energy transferred (J) = power (W) × time (s)

Energy is transferred around a circuit when the charge moves.

energy transferred (J) = charge flow (C) × potential difference (V)

power (W) = potential difference (V) × current (A)

power (W) = (current)(A) × resistance (Ω)

### The National Grid

The National Grid is a system of cables and transformers. They transfer electrical power from the power station to where it is needed. Power stations are able to change the amount of electricity that is produced to meet the demands.

For example, more energy may be needed in homes in the evenings when people come home from work or school. Electricity is transferred at a high potential difference, which reduces the current so less energy is lost as it travels through the cables.

• Step-up transformers – increase the potential difference to make transmission through the cables more efficient.
• Step-down transformers – decrease the potential difference to make it safe for consumers.

## Physics Paper 1 Revision: The Particle Model of Matter

### Density

Density is a measure of how much mass there is in a given volume.

density (kg/m³) = mass (kg) ÷ volume (m³)

A more dense material will have more particles in the same volume when compared to a less dense material.

### Particle Model of Matter

• In solids, the particles are held together very closely in a fixed, regular arrangement. The particles do not have much energy and can only vibrate.
• In liquids, the particles are close together but can move past each other. They form irregular arrangements. They have more energy than the particles in a solid.
• In gases, the particles have the most energy and are free to move in random directions.

### Internal Energy

Particles within a system have a store of kinetic energy when they vibrate or move around. The particles also have a potential energy store.

The total internal energy of a system is the sum of the kinetic and potential energy stores.

If the system is heated, energy is transferred to the kinetic energy store of the particles, so the internal energy of the system increases.

### Changing State

If a system gains more energy, it can lead to a change in temperature or change in state. If a system is heated enough, then there will be enough energy to break bonds.

When something changes state, there is no chemical change, only a physical change. No new substances are formed. The substance will change back to its original form if the conditions are reversed.

The number of particles does not change and mass is conserved.

### Specific Latent Heat

Energy is being put into a system during melting and boiling. This increases the amount of internal energy.

The energy is used to break the bonds between the particles, so the temperature does not increase.

When a substance is condensing or freezing, energy is released as bonds are formed between the particles, so the internal energy decreases. The temperature does not decrease.

Specific latent heat is the amount of energy needed to change the state of 1kg of a substance with no change in temperature.

## Physics Paper 1 Revision: Atomic Structure

### Isotopes

An isotope is an element with the same number of protons but a different number of neutrons. They have the same atomic number, but different mass numbers.

Some isotopes are unstable and, as a result, decay and give out radiation. Ionising radiation is radiation that can knock electrons off atoms. Just how ionising this radiation is, depends on how readily it can do that.

### Alpha

Alpha radiation is an alpha particle emitted from a radioactive nucleus. An alpha particle is made from two protons and two neutrons. Alpha radiation can’t travel very far in the air and is the least penetrating – it can be stopped by skin and paper.

### Beta

Beta radiation is a fast-moving electron emitted from the nucleus that can be stopped by a piece of aluminium. Beta radiation is emitted by an atom when a neutron turns into a proton. The emission of this particle does not cause the mass of the nucleus to change but does cause the charge of the nucleus to increase.

### Gamma

A gamma wave is a type of electromagnetic radiation and is the most penetrating – it is only stopped by thick lead and concrete. The emission of a gamma ray does not cause the mass or the charge of the nucleus to change.

The different types of radiation have different ionising power (the ability to cause atoms or molecules to become charged). Alpha radiation is the most ionising, and gamma is the least ionising.

### Half-life

Half-life is the time taken for the number of radioactive nuclei in an isotope to halve.

Radioactive decay is a random process by which an unstable nucleus gives out radiation as it changes to become more stable – you will not know which nuclei will decay. Radioactive decay is measured in becquerel (Bq). 1Bq is one decay per second.

Irradiation occurs when materials are exposed to a radioactive source. The source is sometimes placed inside a lead-lined box to avoid this.

People who work with radioactive sources will sometimes stand behind a lead barrier, be in a different room or use a remote-controlled arm when handling radioactive substances.

### Contamination

When unwanted radioactive material gets onto an object, that object is said to be contaminated.

Protective clothing should be worn when handling radioactive material.

• Alpha radiation is more dangerous inside the body. It is highly ionising and able to cause a lot of damage. Outside the body it is less dangerous because it cannot penetrate the skin.
• Beta radiation is less dangerous inside the body as some of the radiation is able to escape. Outside the body it is more dangerous as it can penetrate the skin.
• Gamma radiation is the least dangerous inside the body as most will pass out and it is the least ionising. Gamma is more dangerous outside the body as it can penetrate the skin.

## Additional Physics Paper 1 Revision Resources from Beyond

### Physics Assessment Resources and Mock Exams

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