Physics Unit 2: Electricity
GCSE Revision Notes
Circuit symbols: In your GCSE examination you will be expected to recognise the following circuit
symbols and be able to construct circuits using them. Make sure that the wires in your circuit are
straight lines and that the circuit is closed.
Current and charge:
Current: The flow of electrical charge, measured in amperes (A). Electrical charge will only
flow around a complete (closed) circuit if there is a potential difference, so a current can
only flow if there’s a source of potential difference.
We use ammeters to measure the current flowing through a circuit. Ammeters should be
placed in series with whatever you are investigating.
Potential difference: The driving force that pushes the charge around, measured in volts (V).
We use voltmeters to measure the potential difference flowing
through a circuit. Voltmeters should be placed in parallel
around whatever you are investigating.
Resistance: Anything that slows the flow of charge down, measured in ohms (Ω).
The greater the resistance across a component, the smaller the current that flows.
Electrons flow around electrical circuits carrying charge and they are negatively charged.
This means that the electrons flow from negative to positive. However, the current is still
defined as going from positive to negative.
Charge = current x time
Q=Ixt
Q = charge, measured in coulombs.
I = current, measured in amps.
Current in circuits:
In a series circuit, components (e.g. bulbs) occur one after the other (like a TV series).
In a parallel circuit, components (e.g. bulbs) occur on separate branches of the circuit.
, Resistance: Opposition to the flow of charge – the higher the resistance of a circuit, the lower the
current.
The resistance of a circuit can be increased by adding resistors (or variable resistors).
Resistance = potential difference ÷ current.
Voltage = current x resistance
V=IxR
Resistance Required Practical:
1. Take a length of the wire measuring just over one metre, and
connect two crocodile clips to it a distance of 10 cm apart.
2. Connect the wire, using the clips, to the above circuit and measure the
potential difference and current. Use these measurements to calculate the resistance of that
length.
3. Now move the clips 10 cm further apart and take new measurements.
4. Continue up to a length of 1 metre.
5. Now repeat the experiment twice more and take averages of the resistances for each length.
6. Finally, plot a graph of resistance (y-axis) against length (x-axis).
Conclusion: As the length of the wire increases, the resistance increases.
Resistance and IV characteristics Required Practical:
For some components, as the current through them is changed, the resistance of the
component changes as well.
The resistance of ohmic conductors (e.g. a wire or a resistor) doesn’t change with the
current. At a constant temperature, the current flowing through an ohmic conductor is
directly proportional to the potential difference across it.
The term ‘I-V characteristics’ refers to a graph which shows how the current flowing through
a component changes as the potential difference across it increases. Linear components
have an I-V characteristic that is in a straight line (e.g. a fixed resistor). Non-linear
components have a curved I-V characteristic (e.g. a filament lamp or a diode).
GCSE Revision Notes
Circuit symbols: In your GCSE examination you will be expected to recognise the following circuit
symbols and be able to construct circuits using them. Make sure that the wires in your circuit are
straight lines and that the circuit is closed.
Current and charge:
Current: The flow of electrical charge, measured in amperes (A). Electrical charge will only
flow around a complete (closed) circuit if there is a potential difference, so a current can
only flow if there’s a source of potential difference.
We use ammeters to measure the current flowing through a circuit. Ammeters should be
placed in series with whatever you are investigating.
Potential difference: The driving force that pushes the charge around, measured in volts (V).
We use voltmeters to measure the potential difference flowing
through a circuit. Voltmeters should be placed in parallel
around whatever you are investigating.
Resistance: Anything that slows the flow of charge down, measured in ohms (Ω).
The greater the resistance across a component, the smaller the current that flows.
Electrons flow around electrical circuits carrying charge and they are negatively charged.
This means that the electrons flow from negative to positive. However, the current is still
defined as going from positive to negative.
Charge = current x time
Q=Ixt
Q = charge, measured in coulombs.
I = current, measured in amps.
Current in circuits:
In a series circuit, components (e.g. bulbs) occur one after the other (like a TV series).
In a parallel circuit, components (e.g. bulbs) occur on separate branches of the circuit.
, Resistance: Opposition to the flow of charge – the higher the resistance of a circuit, the lower the
current.
The resistance of a circuit can be increased by adding resistors (or variable resistors).
Resistance = potential difference ÷ current.
Voltage = current x resistance
V=IxR
Resistance Required Practical:
1. Take a length of the wire measuring just over one metre, and
connect two crocodile clips to it a distance of 10 cm apart.
2. Connect the wire, using the clips, to the above circuit and measure the
potential difference and current. Use these measurements to calculate the resistance of that
length.
3. Now move the clips 10 cm further apart and take new measurements.
4. Continue up to a length of 1 metre.
5. Now repeat the experiment twice more and take averages of the resistances for each length.
6. Finally, plot a graph of resistance (y-axis) against length (x-axis).
Conclusion: As the length of the wire increases, the resistance increases.
Resistance and IV characteristics Required Practical:
For some components, as the current through them is changed, the resistance of the
component changes as well.
The resistance of ohmic conductors (e.g. a wire or a resistor) doesn’t change with the
current. At a constant temperature, the current flowing through an ohmic conductor is
directly proportional to the potential difference across it.
The term ‘I-V characteristics’ refers to a graph which shows how the current flowing through
a component changes as the potential difference across it increases. Linear components
have an I-V characteristic that is in a straight line (e.g. a fixed resistor). Non-linear
components have a curved I-V characteristic (e.g. a filament lamp or a diode).
