CIE A Level Physics

Topic Questions

A LevelPhysicsCIETopic Questions21. Alternating Currents21.1 Properties and Uses of Alternating Current

Syllabus Edition

First teaching 2020

Last exams 2024

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21.1 Properties and Uses of Alternating Current

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Easy
Medium
Easy
Medium
1a3 marks

For an alternating voltage, state what is meant by 

(i)
the peak voltage,
[1]
(ii)
the root mean square voltage.
[2]

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1b3 marks

A generator produces an alternating voltage which can be described by the equation

V space equals space 150 space sin space open parentheses 200 straight pi t close parentheses

where V is measured in volts and t is in seconds.

For this alternating voltage, determine

 
(i)
the peak voltage,
[1]
(ii)
the r.m.s. voltage,
[1]
(iii)
the frequency.
[1]

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1c6 marks

The alternating voltage is supplied across a 100 Ω resistor.

Calculate

 
(i)
the peak current and hence the r.m.s. current in the resistor,
[2]
(ii)
the mean power dissipated in the resistor,
[2]
(iii)
the peak power dissipated in the resistor.
[2]

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1d1 mark

State the effect on the output voltage if the frequency of the generator is increased.

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2a1 mark

Fig. 1.1a shows an alternating current generator with a rectangular coil rotating at a constant frequency in a uniform magnetic field.

11-2-ib-hl-sqs-easy-q2a-question

Fig. 1.1a

The graph in Fig. 1.1b shows how the output voltage V from the generator varies with time t.

11-2-ib-hl-sqs-easy-q2b-question

Fig. 1.1b

Using Fig. 1.1b, state the peak output voltage V subscript 0 of the generator.

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2b2 marks

Calculate the root mean squared voltage V subscript r m s end subscript.

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2c3 marks

The mean power output of the generator is 35 kW.

Calculate the root mean squared current I subscript r m s end subscript.

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2d2 marks

Draw a line on the graph in Fig. 1.1b to show the Vrms.

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3a2 marks

In rectification, a smoothing capacitor is often necessary.

State the meaning of

  
(i)
rectification,
[1]
(ii)
smoothing.
[1]

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3b4 marks

Fig. 1.1a shows the voltage output from an alternating current supply.

ib-sq-11-3-qu-4b-1

Fig. 1.1a

Sketch the variation of time with output voltage during

 
(i)
half-wave rectification on Fig. 1.1b
 

ib-sq-11-3-qu-4b-2

Fig. 1.1b

[2]

(ii)
full-wave rectification on Fig. 1.1c
 

ib-sq-11-3-qu-4b-2

Fig. 1.1c

[2]

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3c2 marks

A capacitor is placed in parallel with a resistive load to smooth the rectified voltage. The graph of the smoothed output voltage against time gives a 'ripple' shape as shown in Fig. 1.2.

ib-sq-11-3-qu-4c

Fig. 1.2

State how the 'ripples' in the graph can be reduced.

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3d2 marks

Fig. 1.3a shows a diode bridge circuit. It is designed to allow current to flow in certain pathways depending on the input direct of the current.

21-1-3d-21-1-e-diode-bridge-circuit-1-cie-ial-sq

Fig. 1.3a

Draw the path of the current

(i)
on Fig. 1.3b

21-1-3d-21-1-e-diode-bridge-circuit-2-cie-ial-sq

Fig. 1.3b

[1]

(ii)
on Fig. 1.3c

21-1-3d21-1-e-diode-bridge-circuit-3-cie-ial-sq

Fig. 1.3c

[1]

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1a
Sme Calculator2 marks

Alternating current (a.c.) is converted into direct current (d.c.) using a full-wave rectification circuit. Part of the diagram of this circuit is shown in Fig. 1.1.

 
21-1-1a-m-a-c--diodes-input-output-sq-cie-a-level
 Fig. 1.1
 
(i)
On Fig. 1.1, identify the negative output terminal of the rectifier with a (−). 
[1]
 
(ii)
Complete the circuit in Fig. 1.1 by adding the necessary components in the gaps. 
[1]

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1b
Sme Calculator2 marks

The output voltage V of an a.c. power supply varies sinusoidally with time t as shown in Fig. 1.2.

 21-1-1b-m-a-c--graph-find-omega-sq-cie-a-level
Fig. 1.2
 
Determine the equation for V in terms of t, where V is in volts and t is in seconds. 

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1c
Sme Calculator2 marks

The supply is connected to a 25 Ω resistor. Calculate the mean power dissipated in the resistor. 

 
mean power = ............................................. W 

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2a
Sme Calculator2 marks

Fig. 1.1 shows four diodes and a load resistor of resistance, 2.4 kΩ, connected in a circuit that is used to produce rectification of an alternating voltage.

21-1-2a-m-rectification-diodes-resistor-sq-cie-a-level

Fig. 1.1

 

(i)
State what is meant by rectification.
[1]
 
(ii)
State the type of rectification produced by the circuit in Fig. 1.1
[1]

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2b
Sme Calculator4 marks

A sinusoidal alternating voltage VIN is applied across the input terminals X and Y. The variation of time t of VIN is given by the equation

       V subscript I N end subscript space equals space 3.0 space sin space open parentheses 20 pi space t close parentheses
 
where VIN is in volts and t is in seconds.
 
(i)
Label the output terminals A and B, on Fig. 1.1, with the appropriate symbols to indicate the polarity of the output voltage VOUT.
[1]
 
(ii)
The magnitude of the output voltage VOUT varies with t as shown in Fig. 1.2
 
FTgiaqfx_21-1-2b-m-vout-t-to-label-sq-cie-a-level
Fig. 1.2
 
Label both the axis with the correct scales on Fig. 1.2. Use the space below for any working that you need.
 

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2c
Sme Calculator3 marks

The output voltage in (b) is smoothed by adding a capacitor to the circuit in Fig. 1.1. 

The difference between the maximum and minimum values of the smoothed output voltage is 15% of the peak voltage.
 
(i)
On Fig. 1.1, draw the circuit symbol for a capacitor showing the capacitor correctly connected into the circuit.
[1] 
(ii)
On Fig. 1.2, sketch the variation with t of the smoothed output voltage.
[2]

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3a
Sme Calculator2 marks

A sinusoidal alternating voltage has a root-mean square (r.m.s) potential difference (p.d.) of 5.1 V and a frequency of 40 Hz.  

The alternating voltage is applied across a resistor of resistance 1430 Ω. 

Calculate the mean power dissipated by the resistor in mW. 

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3b
Sme Calculator4 marks

On Fig. 1.1, draw a smooth curve to show how the power P dissipated in the resistor varies with time t between t = 0 and t = 100 ms. 

Assume that P = 0 when t = 0.

21-1-3b-m-power-time-graph-axis-sq-cie-a-level

Fig. 1.1

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3c
Sme Calculator3 marks

The alternating voltage in (a) is now applied to a piezoelectric crystal in air. 

Explain what happens to the air surrounding the crystal.

 

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