A LevelPhysicsCIETopic Questions19. Capacitance19.1 Capacitors & Capacitance

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First teaching 2023

First exams 2025

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Capacitors & Capacitance (CIE A Level Physics)

Topic Questions

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1a
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Two capacitors, X and Y, of capacitance 25 μF and 88.5 μF respectively, are connected in parallel to a battery of emf 6.0 V, as shown in Fig. 1.1 

 

7-6-s-q--q4a-easy-aqa-a-level-physics

Fig. 1.1

The plates of both capacitor X and capacitor Y are separated by a vacuum. 

Complete Table 1.1 for this circuit. 

Table 1.1

capacitor

capacitance / μF

p.d. / V

charge / μC

X

25.0

 

 

Y

88.5

 

 

 

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1b
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The total capacitance C subscript t o t a l end subscript for two capacitors C subscript 1 and C subscript 2 connected in parallel is given by the equation: 

C subscript t o t a l end subscript space equals space C subscript 1 space plus space C subscript 2

Using the equation given, calculate the total capacitance of the circuit shown in Fig. 1.1 in Farads, F.

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1c
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A dielectric material is inserted into the space between the plates of capacitor Y in Fig. 1.1. 

State how the capacitance of capacitor Y changes with an added dielectric material.

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1d
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The graph in Fig. 1.2 represents the equation Q = CV.

19-1-e-q1d-sq-cie-ial-physics

Fig. 1.2

State the quantities represented by each axis. 

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2a
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State the relationship between the capacitance of a capacitor and the charge stored. 

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2b
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A parallel plate capacitor X of capacitance 300 μF is fully charged to a potential difference of 8 V. 

Calculate the charge stored by X when it is fully charged.

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2c
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A graph showing how the charge stored Q  by capacitor X varies with the potential difference V  across it is shown in Fig. 1.1.

19-1-e-q2c-sq-cie-ial-physics

Fig. 1.1

State the value of the gradient of the line shown in Fig. 1.1. 

Give a reason for your answer.

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2d
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A parallel plate capacitor Y is placed in series with the parallel plate capacitor X. Capacitor Y has a capacitance of 200 µF.

Calculate the combined capacitance of capacitors X and Y in this arrangement. 

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1a
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Define the capacitance of a parallel plate capacitor.

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1b
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Two capacitors, of capacitances, CA and CB, are connected in parallel to a power supply of electromotive force (e.m.f.) E, as shown in Fig. 1.1.

 19-1-1b-m-capacitors-in-parallel-sq-cie-a-level
Fig. 1.1
 

Determine an expression for the combined capacitance CC of the two capacitors. 

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1c
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Two capacitors of capacitances 18 μF and 51 μF, and resistor of resistance 4.5 kΩ, are connected into the circuit of Fig. 1.2.

 
19-1-1c-m-capacitance-circuit-sq-cie-a-level
Fig. 1.2
 

The battery has an e.m.f of 8 V.

(i)
Calculate the combined capacitance of the two capacitors.
[1]
 
(ii)
The two-way switch S is initially at position P, so that the capacitors are fully charged. 
 
Use the information in (c) (i) to calculate the total energy stored in the two capacitors.
 
total energy = .................................. J [2]

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2a
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Three capacitors, each of capacitance 27 μF, are connected as shown in Fig. 1.1.

 19-1-2a-m-capacitance-circuit-with-series-and-parallel-sq-cie-a-level

 

Fig. 1.1

Calculate the total capacitance between points P and Q.

 
capacitance = ..................................... μF 

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2b
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The maximum safe potential difference that can be applied across any one capacitor is 4 V. 

Determine the maximum safe potential difference that can be applied between points P and Q.

 
potential difference = ...................................... V 

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2c
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A capacitor consists of an insulator separating two metal plates, as shown in Fig. 1.3.

19-1-2c-m-capacitor-with-insulator-sq-cie-a-level

Fig. 1.3

 

The potential difference between the plates is V. The variation with V of the magnitude of the charge Q on one plate is shown in Fig. 1.4.

19-1-2c-m-energy-stored-in-capacitor-graph-sq-cie-a-level

Fig 1.4

Explain why the capacitor stores energy but not charge.

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2d
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Use Fig. 1.4 to determine: 

(i)
the capacitance of the capacitor
 

capacitance = ................................. μF [2]

 

(ii)
the loss in energy stored in the capacitor when the potential difference V is reduced from 8 V to 6 V.
 

energy = ................................. mJ [2]

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3a
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State two functions of capacitors connected in electrical circuits.

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3b
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Three capacitors are connected in parallel to a power supply as shown in Fig. 1.1. 

 19-1-3b-m-show-combined-capacitance-sq-cie-a-level
Fig. 1.1
 

The capacitors have a capacitance CA, CB and CC. The power supply provides a potential difference E. 

(i)
Explain why the charge on the positive plate of each capacitor is different. 
 
[1] 
(ii)
Use your answer in (i) to show that the combined capacitance CT of the three capacitors is given by the expression.
 
C subscript T space equals space C subscript A space plus space C subscript B space plus thin space C subscript C 
[2]

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3c
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A student has available three capacitors, each of capacitance 24 μF. 

Draw circuit diagrams, one in each case, to show how the student connects the three capacitors to provide a combined capacitance of: 

(i)
36 μF
[1] 
(ii)
16 μF

[1]

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