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Capacitors - Multiple Choice

Q1. A 1μF capacitor is charged using a constant current of 10 μA for 20 s.

What is the energy finally stored by the capacitor?

 

A 
2 × 10-3 J
B
2 × 10-2 J
C
4 × 10-2 J
D
4 × 10-1 J

 

Q2. A capacitor of capacitance 10 μF is fully charged through a resistor R to a p.d. of 20V using the circuit shown below.

Which one of the following statements is incorrect?

A The p.d. across the capacitor is 20V.
B The p.d. across the resistor is 0V.
C The energy stored by the capacitor is 2mJ.
D The total energy taken from the battery during the charging process is 2 mJ.

Q3. A 10 mF capacitor is charged to 10V and then discharged completely through a small motor.

During this process, the motor lifts a weight of mass 0.10 kg.

If 10 % of the energy stored in the capacitor is used to lift the weight, through what approximate height will the weight be lifted?

A
0.05 m
B
0.10 m
C
0.50 m
D
1.00 m

 

Q4. A capacitor of capacitance 15 μF is fully charged and the potential difference across its plates is 8.0V. It is then connected into the circuit as shown below.

The switch S is closed at time t = 0.

Which one of the following statements is correct?

A The time constant of the circuit is 6.0 ms.
B The initial charge on the capacitor is 12 μC.
C After a time equal to twice the time constant, the charge remaining on the capacitor is Q0e2, where Q0 is the charge at time t = 0.
D After a time equal to the time constant, the potential difference across the capacitor is 2.9V.

 

Q5. A capacitor of capacitance C discharges through a resistor of resistance R. Which one of the following statements is not true?

A
 The time constant will increase if R is increased.
B
 The time constant will decrease if C increased.
C
 After charging to the same voltage, the initial discharge current will increase if R is decreased.
D
 After charging to the same voltage, the initial discharge current will be unaffected if C is increased.

 

Q6. In the circuit shown below, the capacitor C is charged to a potential difference V when the switch S is closed.

Which line, A to D, in the table gives a correct pair of sketch graphs showing how the charge and current change with time after S is closed?

Charge
Current
A
graph 1
graph 1
B
graph 1
graph 2
C
graph 2
graph 1
D
graph 2
graph 2

 

Q7. The sketch graph shows how the charge stored by a capacitor varies with the potential difference across it as it is charged from a 6V battery.

Which one of the following statements is not correct?

A
 The capacitance of the capacitor is 5.0 μF.
B
 When the potential difference is 2V the charge stored is 10 μC.
C
 When the potential difference is 2V the energy stored is 10 μJ.
D
 When the potential difference is 6V the energy stored is 180 μJ.

 

Q8. A capacitor of capacitance C stores an amount of energy E when the pd across it is V. Which line, A to D, gives the correct stored energy and pd when the charge is increased by 50% ?

 
energy
p.d.
A
1.5E
1.5V
B
2.25E
1.5V
C
1.5E
2.25V
D
2.25E
2.25V


Q9. How many of the following four equations correctly represent the energy E stored by a capacitor of capacitance C when it is charged to a pd V and its charge is Q?

 

E = ½ Q2/C
E = ½ C/V2
E = ½ QC
E = ½ CV2

 

A
one
B
two
C
three
D
four

 

Q10. A voltage sensor and a datalogger are used to record the discharge of a 10 mF capacitor in series with a 500Ω resistor from an initial pd of 6.0V. The datalogger is capable of recording 1000 readings in 10s.

Which line, A to D, in the table gives the pd and the number of readings made after a time equal to the time constant of the discharge circuit?

 
potential difference/V
number of readings
A
2.2
50
B
3.8
50
C
2.2
500
D
3.8
500