Effect-of-Change Questions
Effect-of-Change Questions
- These questions test a causal chain, not a memorised statement such as “more resistance means more voltage”.
- Start with the component that changes and follow the circuit one quantity at a time.
A source with internal resistance
For a fixed e.m.f. and internal resistance:
- external resistance increases → source current decreases;
- lost volts decreases;
- terminal p.d. increases.
Reverse every arrow if the external resistance decreases. A branch current may still behave differently, so identify which current the question asks about.
Write every link in the explanation
Your turn9702/22/O/N/25 Q5(b)(iv)
An LDR is part of the external circuit of a cell with internal resistance. The light intensity decreases. Explain the effect on the terminal p.d. of the cell. [3] (9702/22/O/N/25 Q5)
Show worked answer
The LDR resistance increases, so the total external resistance increases. The source current and lost volts decrease. Therefore the terminal p.d. increases.