Resistance (Edexcel GCSE Combined Science: Physics): Revision Note

Resistance & Current

• Resistors come in two types:

  • Fixed resistors

  • Variable resistors

• Fixed resistors have a resistance that remains constant

• Variable resistors can change the resistance by changing the length of wire that makes up the circuit

  • A longer length of wire has more resistance than a shorter length of wire

• This therefore can vary the amount of current through the circuit:

  • The larger the resistance, the smaller the current

  • The smaller the resistance, the larger the current

• For fixed and variable resistors, once the resistance is set, it will stay at this value no matter how the current changes

• However, the resistance of components such as lamps, diodes (diodes and LEDs), thermistors and LDRs (light dependent resistors) changes with the current through the component

Fixed and variable resistor circuit symbols

Calculating Resistance

• The current, resistance and potential difference of a component in a circuit are calculated using the equation:

• This equation can be rearranged with the help of the following formula triangle:

Voltage, current, resistance formula triangle