GCSE PHYSICS - ELECTRICITY

What is electric current?

The flow of electrical charge.

State the equation linking charge, current and time. Give the units for the quantities involved.

Q = I t
Charge (Coulombs), Current (Amperes), Time (Seconds)

What can be said about the value of
current at any point in a single closed loop?

Current is the same at all points in a closed loop.

What two factors does the current in a
circuit depend on?

1. Potential Difference (V)
2. Resistance (R)

What equation should be used to
calculate potential difference if current
and resistance are known? State the
units for all 3 quantities.

V = I R
Potential Difference (V), Current (A), Resistance (Ω)

What is an ‘Ohmic Conductor’? State the
condition required.

● A conductor for which current and potential difference are directly proportional
● Resistance remains constant as current changes
● Temperature must be constant

List four components for which
resistance is not constant as current
changes

1. Lamps
2. Diodes
3. Thermistors
4. Light Dependant Resistors (LDRs)

What happens to the resistance of a
filament lamp as the temperature increases? Why?

● Resistance increases
● Ions in metal have more energy, so vibrate more, causing more collisions with electrons as they flow through the metal, creating greater resistance to current flow

What is different about current flow through a diode?

● The current only flows in one direction
● Resistance is very high in the other direction, preventing current flow

State what happens to the resistance of
a thermistor as temperature increases.

The thermistor’s resistance decreases.

Give two examples of when a thermistor
may be used.

1. In a thermostat to turn a heater on below a certain temperature
2. In a freezer to turn on a cooler when the temperature becomes too high

State what happens to the resistance of
a LDR as light intensity decreases.

The LDR’s resistance increases.

What are the two ways that a component
can be connected in a circuit?

1. Series (same loop)
2. Parallel (adjacent loop)

How does the potential difference across
two components vary when connected in
series and parallel?

● Series: Total P.D is shared between each component
● Parallel: P.D across each component is the same

If two resistors are connected in parallel,
what can be said about their combined
total resistance?

Their total resistance is less than the smallest of the two individual
resistances.

If two resistors are connected in series,
what can be said about their total
resistance?

Their total combined resistance is equal to the sum of the two individual resistances.

Describe the current in a series circuit.

In a series circuit, the current is the same at all positions since the charge only has one path to flow through.

Describe the current in a parallel circuit.

In a parallel circuit, the current is shared between the different branches. When the charge reaches a junction it splits.

How should you connect an ammeter in
a circuit to measure current?

Ammeters should be connected in series with the component that they are measuring current through.

How should you connect a voltmeter in a
circuit to measure potential difference?

Voltmeters should be connected in parallel to the component that they are measuring the potential difference of.

Why is it advantageous to connect lamps
in parallel?

If one lamp blows, the rest will be unaffected and can still receive current (i.e. the circuit is still complete).

Is mains electricity an a.c supply or a d.c
supply? What do each of these stand
for?

Mains electricity is an a.c supply
a.c. : Alternating Current
d.c. : Direct Current

Define alternating current and direct
current.

● Alternating current: Current that continuously changes direction at a specific frequency
● Direct current: One directional current flow

What is the frequency and voltage of the
UK mains electricity supply?

● Frequency: 50 Hz
● Voltage: 230V

How many wires are usually in the
cables connecting electrical appliances
to the mains? Name these wires.

1. Live wire
2. Neutral wire
3. Earth wire

State the insulation colour used on the
Earth wire.

Green and Yellow Stripes

State the insulation colour used on the
live wire.

Brown

State the insulation colour used on the
neutral wire.

Blue

Explain when the Earth wire does and
doesn’t carry a current.

● Under normal circumstances, no current flows through the Earth wire
● If a fault occurs in the appliance (such as a surge or the casing becoming live), current will flow to the ground

What potential is the neutral wire at?

0 Volts

State the potential difference between
the live and earth wires

230 Volts

What is the purpose of the neutral wire?

To complete the circuit by connecting the
appliance back to the mains supply.

For metal appliances, where is the Earth
wire connected to? Why?

● Earth wire is connected to the metal casing of the appliance
● If live wire becomes loose and touches the casing, the current will flow through the Earth wire, preventing electrocution

State two equations for the power of a
circuit. Give appropriate units.

P = I V
P = I² R
Power (Watts), Current (Amperes) Potential Difference (Volts), Resistance (Ohms)

State an equation linking energy transferred, power and time. Give
appropriate units.

E = P t
Energy (Joules), Power (Watts), Time (Seconds)

State an equation linking energy
transferred, charge flow and potential
difference. Give appropriate units.

E= Q V
Energy (Joules), Charge (Coulombs), Potential Difference (Volts)

What two main factors does the amount
of energy transferred by an appliance
depend on?

1. How long the appliance is being used for
2. The power of the appliance

What three things determine the power
of a circuit device?

1. The potential difference across the circuit
2. The current through the circuit
3. The amount of energy transferred in a given time

What is the purpose of the National Grid?

To link power stations to consumers so that they have access to a source of electricity.

What are the two types of transformers
used in the National Grid?

1. Step-Up Transformers
2. Step-Down Transformers

Where are step-up transformers found in
the National Grid? What do they do?

● Step-Up Transformers are used when connecting power stations to
transmission cables
● They increase the potential difference

Where are step-down transformers found
in the National Grid? What do they do?

● Step-Down Transformers are used in connecting transmission cables to domestic buildings (like houses)
● They decrease the potential difference

Why do transmission lines transfer
electricity at high potentials?

● A high potential, results in a low current
● The lower the current, the less energy that is wasted as heat
● Therefore it is more efficient

Why does the potential need to be
decreased between transmission lines
and houses?

● Lower potentials are safer for domestic use and reduces the likelihood of severe electrocution
● Appliances are designed for 230V

What can happen when insulating
materials are rubbed together?

They can become (statically) electrically charged.

Why can insulators become electrically
charged when rubbed together?

● Electrons are rubbed from one material onto the other
● The material gaining electrons becomes negatively charged
● The material losing electrons becomes equally positively charged

What happens when two electrically
charged objects are brought close together?

They exert a force on each other.

What happens when two identically
charged objects are brought close
together?

They exert a repulsive force on each other and repel.

What happens when two oppositely
charged objects are brought close
together?

They exert an attractive force on each other and attract

Give an example of a non-contact force.

The repulsive or attractive force acting between two electrically charged objects.

What is an electric field?

A region in which a charged object will experience a non-contact electrical force.

Where can electric fields be found?

Surrounding any charged object.

Describe the electric field around a
charged particle.

● Strongest closest to the object
● Decreases in strength as you move away from the object

What happens to the force between two
charged objects when they are moved
closer together?

The force between them becomes stronger as the separation reduces

In situations where sparks are unwanted,
what precaution must be taken to
prevent the build up of static charge?

Any surfaces that are rubbing against each other should be earthed to allow the charge to flow off the materials.