Pearson Edexcel · GCSE · Physics
Course version: 1PH0 · Version from Sept 2016
Explain how changing the resistance in a circuit changes the current and…
Full specification wording
Topic 10 – Electricity and circuits: 10.12 Explain how changing the resistance in a circuit changes the current and how this can be achieved using a variable resistor
For a fixed potential difference, current and resistance are inversely related: increasing resistance reduces current, and decreasing resistance increases it.
Checked against the Pearson Edexcel 1PH0 specification (opens in a new tab) on .
- Point 12 of 39
Study notes
From the checked teaching notes for this specification point.
The idea
For a fixed potential difference, current and resistance are inversely related: increasing resistance reduces current, and decreasing resistance increases it. This follows from I = V ÷ R, so doubling R halves I when V stays constant. A variable resistor (rheostat) lets you change resistance continuously, for example to dim a lamp or control a motor's speed. Turning or sliding it changes the length or amount of resistive material in the circuit, altering the resistance. In questions, state the direction of the change, link it to I = V ÷ R, and name the variable resistor as the means of achieving it.
What earns the marks
- States that increasing the resistance decreases the current for a fixed potential difference.
- States that decreasing the resistance increases the current for a fixed potential difference.
- Links the change to the relationship current = potential difference ÷ resistance.
- Identifies a variable resistor as a component whose resistance can be changed to control the current.
Common mistakes and how to put them right
Claims that increasing resistance increases the current.
Put it right: Increasing resistance reduces the current at fixed potential difference.
Forgets that the potential difference must be held constant for the inverse relationship to hold.
Put it right: State this condition.
Describes a variable resistor as changing the voltage supply.
Put it right: It changes the resistance in the circuit.
Exam tips
- Quote the equation current = potential difference ÷ resistance to justify the direction of change.
- Say explicitly that the potential difference is kept constant when explaining the effect on current.
- Name the variable resistor and describe how adjusting it alters the resistance.
Try the lesson
The start of the Topic 10 – Electricity and circuits: 10.12 Explain how changing the resistance in a circuit changes the current and how this can be achieved using a variable resistor lesson, made from checked teaching notes for this specification point.
Have a go first
A fixed battery is connected to a circuit. If the resistance of the circuit is increased, what happens to the current?
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