10 questions🇬🇧English
🔋 Capacitor Charge & Discharge – A-level
Physics · A-level — capacitance, stored energy, the time constant RC and exponential charging and discharging
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Questions
A 470 μF capacitor is charged to a potential difference of 12 V. How much charge is stored on it?
39.2 μC
56.4 mC
5.64 mC
2.82 mC
20s
A capacitor discharges through a resistor. What does the area under its current–time graph represent?
The charge that flowed off the capacitor
The energy that was stored in the capacitor
The capacitance of the capacitor
The time constant of the circuit
20s
How much energy is stored in a 100 μF capacitor charged to 20 V?
1 mJ
40 mJ
20 mJ
2 mJ
30s
A 6 μF capacitor and a 3 μF capacitor are connected in series. What is their combined capacitance?
4.5 μF
0.5 μF
9 μF
2 μF
30s
A 220 μF capacitor discharges through a 10 kΩ resistor. What is the time constant of the circuit?
45 s
2.2 s
22 s
0.22 s
30s
A capacitor discharges through a resistor. What percentage of its initial charge remains after one time constant?
About 50%
About 14%
About 63%
About 37%
20s
A parallel-plate capacitor stays connected to a battery. A dielectric with εr = 3 then fills the gap. What happens to the charge stored?
It stays the same
It falls to a third
It triples
It increases ninefold
30s
A capacitor discharges through a resistor with RC = 2.0 s. Roughly how long does its p.d. take to fall to one-eighth of its initial value?
About 2.8 s
About 6.0 s
About 4.2 s
About 16 s
60s
A 100 μF capacitor discharges through a resistor R. A graph of ln V against t has gradient −0.25 s⁻¹. What is R?
25 kΩ
40 kΩ
2.5 kΩ
400 kΩ
60s
An uncharged capacitor is fully charged by a battery through a resistor. What fraction of the energy supplied by the battery is stored?
One quarter
About 63%
All of it
One half
30s