Capacitor charge and discharge NNN

A capacitor of capacitance 120 μF is charged and then discharged through a 20 kΩ resistor. What fraction of the original charge remains on the capacitor 4.8 s after the discharge begins?

• 0.14

• 0.37

• 0.63

• 0.86

A 500 µF capacitor is charged to a voltage of 10.0 V. It is then discharged through a 100 kΩ resistor.

What is the time taken for the voltage to fall from 10.0 V to 5.0 V?

• 35 s

• 50 s

• 72 s

• 100 s

When fully charged the 2.0 mF capacitor used as a backup for a memory unit has a potential difference of 5.0 V across it. The capacitor is required to supply a constant current of 1.0 μA and can be used until the potential difference across it falls by 10%. For how long can the capacitor be used before it must be recharged?

• 10 s

• 100 s

• 200 s

• 1000 s

The voltage across a capacitor falls from 10 V to 5 V in 48 ms as it discharges through a resistor. What is the time constant of the circuit?

• 24 ms

• 33 ms

• 69 ms

• 96 ms

When a capacitor discharges through a resistor it loses 50% of its charge in 10 s. What is the time constant of the capacitor-resistor circuit?

• 0.5 s

• 5 s

• 14 s

• 17 s

A 1000 μF capacitor, initially uncharged, is charged by a supposedly steady fixed current of 50 μA. How long will it take for the potential difference across the capacitor to reach 2.5 V?

• 20 s

• 50 s

• 100 s

• 400 s

The graph shows the variation of potential difference V with time t across a 470 μF capacitor discharging through a resistor.

The resistance of the resistor is approximately

• 900 Ω

• 1300 Ω

• 1900 Ω

• 4700 Ω

A capacitor discharges through a fixed resistor. The time constant τ for the capacitor and resistor is 10 seconds. At what time will the charge across the capacitor have dropped to half the original value?

• 0.5 e^-10

• 10 e^-0.5

• 10 ln(-0.5)

• -10 ln(0.5)

A capacitor discharge circuit of time constant 45 ms includes a capacitor and resistor. The capacitor has a capacitance of 18 µF.

What is the resistance of the resistor?

• 2.5 x 10³ Ω

• 2.5 Ω

• 0.40 Ω

• 4.0 x 10^-4 Ω

In the RC circuit, the time constant (τ) for the circuit is:

• τ = R × C
• τ = R / C
• τ = C × R
• τ = R² × C