Physics Paper 1

AQA GCSE Physics Paper 1 — Higher Notes

AQA Physics Paper 1 covers Topics 1–4:

Energy
Electricity
Particle model of matter
Atomic structure

1. ENERGY

Energy stores

Energy can be stored in:

Thermal
Kinetic
Gravitational potential
Elastic potential
Chemical
Magnetic
Electrostatic
Nuclear

Energy is transferred mechanically, electrically, by heating or by radiation.

Energy equations

Kinetic energy

Ek = ½mv²

Ek = kinetic energy in J
m = mass in kg
v = velocity in m/s

Gravitational potential energy

Ep = mgh

m = mass in kg
g = gravitational field strength, usually 9.8 N/kg
h = height in m

Elastic potential energy

Ee = ½ke²

k = spring constant in N/m
e = extension in m

Power

Power = energy transferred ÷ time

P = E ÷ t

Power is measured in watts (W).

Efficiency

Efficiency = useful energy output ÷ total energy input

For percentage efficiency:

Efficiency × 100

Conservation of energy

Energy cannot be created or destroyed.

It is transferred between stores.

Some energy may be transferred to the surroundings, often by heating, making it dissipated.

Energy resources

Renewable

Wind
Solar
Hydroelectric
Tidal
Wave
Geothermal
Biofuel

Non-renewable

Coal
Oil
Gas
Nuclear fuel

Fossil fuels

Advantages:

Reliable
High energy output
Easy to control

Disadvantages:

Produce CO₂
Contribute to climate change
Finite resources

Nuclear

Advantages:

Large energy output
No CO₂ produced during operation

Disadvantages:

Radioactive waste
Expensive to build
Risk associated with radioactive materials

2. ELECTRICITY

Charge

Charge is measured in coulombs (C).

Current

Current is the rate of flow of charge.

Q = It

Q = charge in C
I = current in A
t = time in s

Potential difference

Potential difference is the energy transferred per unit charge.

V = E ÷ Q

V = potential difference in volts
E = energy in joules
Q = charge in coulombs

Resistance

V = IR

V = voltage
I = current
R = resistance

Resistance is measured in ohms (Ω).

Series Circuits

In a series circuit:

Current is the same everywhere
Potential difference is shared between components
Total resistance is the sum of individual resistances

Rtotal = R₁ + R₂ + R₃

If one component breaks, the whole circuit stops working.

Parallel Circuits

In a parallel circuit:

Potential difference is the same across each branch
Current is shared between branches
Total current = sum of currents in branches

If one branch breaks, the other branches can still work.

Current-Voltage Graphs

Fixed resistor

At constant temperature:

Current is directly proportional to potential difference.

Graph is a straight line through the origin.

Filament lamp

As current increases:

Temperature increases
Resistance increases
Graph becomes less steep

Diode

Current only flows significantly in one direction
Has very high resistance in the opposite direction

Resistance of a Wire

Resistance increases when:

Wire is longer
Wire is thinner

Resistance decreases when:

Wire is shorter
Wire is thicker

Temperature can also affect resistance.

Electrical Power

P = VI

Also:

P = I²R

P = V²/R

Power is measured in watts.

Electrical Energy

E = Pt

Also:

E = QV

For household electricity:

Energy transferred = power × time

National Grid

Electricity is transmitted at a high potential difference.

This allows the current to be lower for the same power.

Lower current means less energy is wasted as heating in the cables.

Transformers

Step-up transformer

Increases potential difference
Decreases current

Step-down transformer

Decreases potential difference
Increases current

Transformers work with AC, not DC.

Mains Electricity

UK mains supply:

Approximately 230 V
Frequency = 50 Hz
AC

Wires

Live

Brown
Carries alternating potential difference

Neutral

Blue
Completes the circuit

Earth

Green/yellow
Safety wire
Protects against electric shock

3. PARTICLE MODEL OF MATTER

Density

Density = mass ÷ volume

ρ = m/V

Units commonly:

kg/m³
g/cm³

Changes of State

Melting

Solid → liquid

Freezing

Liquid → solid

Evaporation

Liquid → gas

Condensation

Gas → liquid

Sublimation

Solid → gas

Internal Energy

Internal energy is the total:

Kinetic energy + potential energy of particles

When temperature increases:

Particles gain kinetic energy.

During a change of state:

Energy is transferred to potential energy.
Temperature remains constant.

Specific Heat Capacity

Specific heat capacity is the energy required to raise the temperature of 1 kg of a substance by 1°C.

ΔE = mcΔθ

ΔE = energy transferred in J
m = mass in kg
c = specific heat capacity in J/kg°C
Δθ = temperature change in °C

Specific Latent Heat

Specific latent heat is the energy required to change the state of 1 kg of a substance without changing its temperature.

E = mL

E = energy in J
m = mass in kg
L = specific latent heat in J/kg

Specific latent heat of fusion

Changing:
solid ↔ liquid

Specific latent heat of vaporisation

Changing:
liquid ↔ gas

Gas Pressure

Gas pressure is caused by particles colliding with the walls of their container.

Increasing temperature causes particles to move faster.

If volume stays constant:

Higher temperature → higher pressure

If temperature stays constant:

Smaller volume → higher pressure

4. ATOMIC STRUCTURE

Structure of an atom

Atoms contain:

Protons
Neutrons
Electrons

Charges

Particle	Charge	Relative mass
Proton	+1	1
Neutron	0	1
Electron	−1	Very small

Isotopes

Isotopes are atoms of the same element with:

Same number of protons
Different number of neutrons

Some isotopes are radioactive.

Radioactivity

Some atomic nuclei are unstable and emit radiation.

Three types:

Alpha

2 protons + 2 neutrons
Strongly ionising
Short range
Stopped by paper/skin
Deflected by electric and magnetic fields

Beta

Fast-moving electron
Moderately ionising
Medium range
Stopped by thin aluminium
Deflected by electric and magnetic fields

Gamma

Electromagnetic radiation
Weakly ionising
Very penetrating
Reduced by thick lead/concrete
Not deflected by electric or magnetic fields

Order of penetration

Alpha < beta < gamma

Order of ionising power

Alpha > beta > gamma

Nuclear Equations

You need to conserve:

Mass number
Atomic number

Alpha decay

Mass number decreases by 4.

Atomic number decreases by 2.

Beta decay

Mass number stays the same.

Atomic number increases by 1.

Half-Life

Half-life is the time taken for the number of unstable nuclei in a sample to halve.

It can also describe the decrease in activity/count rate.

Example:

800 → 400 → 200 → 100

Each step represents one half-life.

Background Radiation

Sources include:

Rocks
Radon gas
Cosmic rays
Medical sources
Food and living organisms

When measuring radiation, subtract background radiation if required:

Corrected count rate = measured count rate − background count rate

Irradiation vs Contamination

Irradiation

An object is exposed to radiation.

It does not become radioactive as a result.

Contamination

Radioactive material gets onto or inside an object.

The object/material can then emit radiation.

Uses of Radiation

Medical tracers

A radioactive isotope is introduced into the body.

A gamma emitter is useful because gamma radiation can escape the body and be detected.

Radiotherapy

Radiation is used to destroy cancer cells.

Smoke detectors

Use a small radioactive source to detect smoke.

Fission

A large unstable nucleus absorbs a neutron and splits into smaller nuclei.

This releases:

Energy
More neutrons

The released neutrons can cause further fission.

This creates a chain reaction.

Fusion

Two small nuclei join to form a larger nucleus.

This releases a large amount of energy.

Fusion occurs naturally in stars.

It requires extremely high temperatures and pressures.

Required Practical: Density

Method for a regular object

Measure the object’s mass using a balance.
Measure its dimensions using a ruler/calipers.
Calculate its volume.
Calculate density:

Density = mass ÷ volume

Method for an irregular object

Measure the mass.
Measure the initial volume of water in a measuring cylinder.
Fully submerge the object.
Record the new volume.
Calculate the object’s volume:

Object volume = final volume − initial volume

Calculate density.

Improvement: Use a displacement can or more precise equipment where appropriate.

Required Practical: Specific Heat Capacity

Measure the mass of the material.
Place an electric heater in the material.
Attach a thermometer.
Insulate the material to reduce energy loss.
Measure the initial temperature.
Switch on the heater.
Record the potential difference and current.
Heat for a measured time.
Record the final temperature.
Calculate energy transferred:

E = VIt

Calculate temperature change.
Calculate specific heat capacity:

c = E ÷ (mΔθ)

Improvements

Insulate the apparatus.
Use a lid.
Reduce heat loss to surroundings.
Stir the material if appropriate so the temperature is more uniform.

Required Practical: Resistance

Investigating resistance of a wire

Set up a circuit containing:
- Power supply
- Ammeter
- Wire
- Voltmeter
Change the length of the wire.
Measure the current.
Measure the potential difference.
Calculate resistance:

R = V ÷ I
6. Repeat for different wire lengths.
7. Keep other variables constant.

Control variables

Material
Thickness
Temperature
Potential difference/current, depending on method

Required Practical: I-V Characteristics

Set up a circuit with the component, ammeter and power supply.
Connect a voltmeter across the component.
Adjust the potential difference.
Record the current and voltage.
Repeat for a range of voltages.
Reverse the polarity if required.
Plot a graph of current against potential difference.

Know the shapes for:

Fixed resistor
Filament lamp
Diode

Required Practical: Radiation

When investigating radiation:

Use a suitable radioactive source.
Measure the background count rate.
Place the detector at a measured distance.
Measure the count rate for a fixed time.
Repeat measurements.
Calculate a mean.
Subtract background radiation where required.
Change one variable, such as distance or absorber thickness.
Keep the measurement time and other variables constant.

Safety

Keep exposure time short.
Maximise distance from the source.
Use shielding where appropriate.
Follow teacher/laboratory instructions.

Formula Sheet to Memorise

Ek = ½mv²

Ep = mgh

Ee = ½ke²

P = E/t

Efficiency = useful output ÷ total input

Q = It

V = E/Q

V = IR

P = VI

P = I²R

P = V²/R

E = Pt

ρ = m/V

ΔE = mcΔθ

E = mL

c = E/(mΔθ)

R = V/I

Higher-Tier Exam Traps

Always convert g → kg when using SI equations.
Convert cm³ → m³ when required.
Convert minutes → seconds for power calculations.
Convert kWh → J if the question asks for joules.
Check whether a question wants energy, power, or efficiency.
For half-life, halve the activity/count, not necessarily the time.
In a series circuit, current is the same everywhere.
In parallel, potential difference is the same across each branch.
Alpha is the most ionising, gamma is the most penetrating.
During a change of state, temperature stays constant while energy changes the arrangement/separation of particles.