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

Syllabus Edition

First teaching 2020

Last exams 2024

|

Properties and Uses of Alternating Current (CIE A Level Physics)

Exam Questions

55 mins6 questions
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]

How did you do?

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]

How did you do?

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]

How did you do?

1d1 mark

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

How did you do?

Did this page help you?

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.

How did you do?

2b2 marks

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

How did you do?

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.

How did you do?

2d2 marks

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

How did you do?

Did this page help you?

3a2 marks

In rectification, a smoothing capacitor is often necessary.

State the meaning of

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

How did you do?

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]

How did you do?

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.

How did you do?

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]

How did you do?

Did this page help you?

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]

How did you do?

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. 

How did you do?

1c
Sme Calculator2 marks

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

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

How did you do?

Did this page help you?

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]

How did you do?

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.
 

How did you do?

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]

How did you do?

Did this page help you?

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. 

How did you do?

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

How did you do?

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.

 

How did you do?

Did this page help you?