CAIE A-Level Physics A2 21.2 Rectification and Smoothing Questions

Practise explaining half-wave and bridge rectification, analysing capacitor smoothing and relating capacitance, load resistance and ripple.

Exam points

distinguish and explain half-wave and bridge full-wave rectification
analyse capacitor smoothing and the effects of capacitance, load resistance and ripple

Covered syllabus points

21.2.1—Distinguish graphically between half-wave and full-wave rectification 21.2.2—The use of a single diode for the half-wave rectification of an alternating 21.2.3—The use of four diodes (bridge rectifier) for the full-wave rectification of 21.2.4—The effect of a single capacitor in smoothing

[Maximum number: 9]

Four diodes are used in a bridge rectifier circuit to produce rectification of a sinusoidal a.c. input voltage $V_{\text {IN }}$ .
Fig. 7.1 shows part of the circuit, but three of the diodes are missing.

Fig. 7.1

The p.d. across the load resistor R is the output p.d. $V_{\text {OUT }}$ of the bridge rectifier.

(a)

State the name of the type of rectification produced by a bridge rectifier.

[ 1 ]

(b)

Complete Fig. 7.1 by drawing the three missing diodes, correctly connected.

[ 2 ]

(c)

On Fig. 7.1, draw an arrow to indicate the direction of the current in resistor R .

[ 1 ]

(d)

$V_{\text {IN }}$ has amplitude $V_{0}$ and period T. Fig. 7.2 shows the variation with time t of $V_{\text {IN }}$ .

Fig. 7.2

[ 5 ]

(i)

On Fig. 7.3, sketch the variation of $V_{\text {OUT }}$ with t between t=0 and t=2.0 T.

Fig. 7.3

[ 3 ]

sketch: periodic line showing minimum $V_{\text {OUT }}=0$ and maximum $V_{\text {OUT }}=+V_{0}$
line showing peak $V_{\text {OUT }}$ at t=0,0.5 T, 1.0 T, 1.5 T and 2.0 T, with $V_{\text {OUT }}$ going to zero half-way in between each peak
line showing correct modulated sine shape

(ii)

The power dissipated in the resistor is P.

On Fig. 7.4, sketch the variation of P with t between t=0 and t=2.0 T.

Fig. 7.4

[ 2 ]

[Maximum number: 4]

Part of an electric circuit is shown in Fig. 5.1.

Fig. 5.1

The circuit is used to produce half-wave rectification of an alternating voltage of potential difference (p.d.) $V_{\text {IN }}$ .

The output p.d. across the $14 \mathrm{k} \Omega$ resistor is $V_{\text {OUT }}$ .

(a)

A component is missing from the circuit of Fig. 5.1.

Complete the circuit diagram in Fig. 5.1 by adding the circuit symbol for the missing component, correctly connected.

[ 1 ]

(b)

A capacitor C is shown in the circuit of Fig. 5.1.

State the effect on $V_{\text {OUT }}$ of including the capacitor in the circuit.

[ 1 ]

smoothing / $V_{\text {out }}$ is smoothed

(c)

The circuit of Fig. 5.1 is modified so that it produces full-wave rectification of an input voltage. Suggest, with a reason, how $V_{\text {OUT }}$ now varies with time when $V_{\text {IN }}$ is as shown in Fig. 5.2.

[ 2 ]

$V_{\text {IN }}$ has constant magnitude in both positive and negative directions
(so) $V_{\text {out }}$ is (now) constant / $V_{\text {out }}$ does not vary with time

[Maximum number: 12]

Fig. 5.1 shows four diodes and a load resistor of resistance $1.2 \mathrm{k} \Omega$ , connected in a circuit that is used to produce rectification of an alternating voltage.

Fig. 5.1

(a)

State what is meant by rectification.

[ 1 ]

(b)

State the type of rectification produced by the circuit in Fig. 5.1.

[ 1 ]

(c)

A sinusoidal alternating voltage $V_{\text {IN }}$ is applied across the input terminals X and Y. The variation with time t of $V_{\text {IN }}$ is given by the equation

V_{\text {IN }}=6.0 \sin 25 \pi t

where $V_{\text {IN }}$ is in volts and t is in seconds.

[ 4 ]

(i)

On Fig. 5.1, label the output terminals P and Q with the appropriate symbols to indicate the polarity of the output voltage $V_{\text {OUT }}$ .

[ 1 ]

(ii)

The magnitude of the output voltage $V_{\text {OUT }}$ varies with t as shown in Fig. 5.2.

Fig. 5.2

On Fig. 5.2, label both of the axes with the correct scales. Use the space below for any working that you need.

[ 3 ]

$V_{\text {Out }}$ scale labelled 4 and 8 on the 2 cm tick marks
$\begin{aligned} T =2 \pi / \omega =2 \pi / 25 \pi =0.08 \mathrm{~s} \end{aligned}$
t scale labelled 0.02,0.04,0.06,0.08,0.10,0.12 on the 2 cm tick marks

(d)

The output voltage in (b) is smoothed by adding a capacitor to the circuit in Fig. 5.1. The difference between the maximum and minimum values of the smoothed output voltage is 10 % of the peak voltage.

[ 6 ]

(i)

On Fig. 5.1, draw the circuit symbol for a capacitor showing the capacitor correctly connected into the circuit.

[ 1 ]

correct symbol used for capacitor and capacitor connected in parallel with the $1.2 \mathrm{k} \Omega$ resistor.

(ii)

On Fig. 5.2, sketch the variation with t of the smoothed output voltage.

[ 2 ]

straight lines or curves, with negative decreasing gradients, drawn between adjacent peaks, from top of first peak to meet
line going up to next peak
lines, from one peak to the line going up to the next peak, show a drop in p.d. of $1 \frac{1}{2}$ small squares

(iii)

Calculate the capacitance C of the capacitor.

[ 3 ]

$V=0.90 \times 6.0(=5.4 \mathrm{~V})$

or

discharge time (for each cycle) $=0.034 \mathrm{~s}$ $V=V_{0} \exp (-t / R C)$ $5.4=6.0 \exp \left[-0.034 /\left(1.2 \times 10^{3} \times C\right)\right]$ $C=2.7 \times 10^{-4} \mathrm{~F}$

[Maximum number: 1]

Part of an electric circuit is shown in Fig. 5.1.

Fig. 5.1

A component is missing from the circuit of Fig. 5.1.

Complete the circuit diagram in Fig. 5.1 by adding the circuit symbol for the missing component, correctly connected.

All question bank results loaded

Covered syllabus points

Question 1

Question (a)

Question (b)

Question (c)

Question (d)

Question (i)

Question (ii)

Question 2

Question (a)

Question (b)

Question (c)

Question 3

Question (a)

Question (b)

Question (c)

Question (i)

Question (ii)

Question (d)

Question (i)

Question (ii)

Question (iii)

Question 4