Intelligent assessment and revision tools for OCR A Physics

In a lab test, a 1000 μF capacitor is charged to 6.0 V, then allowed to discharge through a resistor while a data logger records the voltage. In trial 1 the resistor is 1.0 kΩ; in trial 2 it is 2.0 kΩ. Students measure the time taken for the voltage to drop to 3.0 V. Which statement must be true?

• A Trial 2 takes twice as long; t2 ≈ 2 t1, because for the same capacitor the time to reach the same fraction of the initial voltage is proportional to the resistance.
• B Trial 1 takes twice as long; t1 ≈ 2 t2, because the larger current in trial 1 makes the voltage fall more slowly.
• C Both trials take the same time, because the voltage halves by the same amount regardless of the resistor used.
• D Trial 2 takes four times as long; t2 ≈ 4 t1, because reducing the current leads to a squared increase in the time.