Q1.
Capacitor questions - A2 Physics
The graph shows how the charge of a capacitor varies with the p.d. across it.
Use the graph to find
a) the energy stored by the capacitor when charged to a potential difference of 8 V
(2 Marks)
b) the capacitance of the capacitor
(2 Marks)
Q2.
The diagram below shows a circuit diagram of a capacitor discharging through a resistor.
A simple mathematical model of the discharge of the capacitor is shown in the block diagram below. It is assumed
that the current I is constant over each small time interval Δt. The process is repeated as shown.
LOJ - 2011
1
Capacitor questions - A2 Physics
Copy and complete the table for the discharge of the 4700μF capacitor. The small time interval used is Δt = 2.0 s.
(3 Marks)
Q3.
In the circuit below the capacitor is charged to a potential difference of 6.0 V.
When the switch is moved from A to B , the capacitor discharges
through the resistor.
a) Show that the initial value of the discharge current is about 1
mA.
(2 Marks)
b) The time constant RC of the discharge circuit is about 26 s.
Calculate the current in the discharge circuit after the switch
has been closed for a time equal to RC.
(2 Marks)
(4 marks)
Q4.
What is the energy stored by a 33 000 mF capacitor charged to 10.0 V? (2 marks)
Q5.
What is the charge held by a 500 mF capacitor charged to a p.d. of 3.5 V? (2 marks)
Q6.
A capacitor is connected to a 9V power supply by a reed switch operating at 300 Hz. The ammeter reads
37 mA. What is the capacitance of the capacitor? (2 marks)
Q7.
5000 mF capacitor is charged to 9.0 V and discharged through a 2700  resistor.
(a) What is the time constant? (1 mark)
(b) What is the voltage after 3 s? (2 marks)
(c) What is the half-life of the decay? (2 marks)
(d) How long would it take the capacitor to discharge to 2.0 V (3 marks)
LOJ - 2011
(8 marks)
2