Charging and discharging capacitorsEdexcel International A Level Physics: Mind map

Exam questions on Charging and discharging capacitors

1. A 2200 μF capacitor is charged to a p.d. of 9.0 V and is then discharged through a 4.7 kΩ resistor.
   Calculate the p.d. across the capacitor 20 s after the discharge begins.2 marks
2. A 100 μF capacitor, initially uncharged, is charged through a 47 kΩ resistor using a 6.0 V supply that has negligible internal resistance.
   Explain why the current in the circuit decreases as the capacitor charges.2 marks
3. In Core Practical 11 a student records the p.d. V across a capacitor as it discharges through a resistor, using a data logger. She plots ln V against the time t in seconds (V in volts). Her line of best fit is straight, with a gradient of −0.050 s⁻¹ and an intercept of 2.20 on the ln V axis.
   Use the equation for exponential discharge to explain the shape of her graph, and determine the time constant of the circuit and the initial p.d. across the capacitor.3 marks