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CAIE A-Level Physics 21 Alternating Currents

Practise analysing sinusoidal a.c. values and power, rectification paths and smoothing behaviour in a practical rectified supply.

Syllabus
2028–2030
Course
Physics 9702
Level
A2

Exam points

  • calculate and interpret sinusoidal current and voltage parameters, rms values and power
  • analyse half-wave/full-wave rectification and diode conduction paths
  • explain and calculate smoothing behaviour in rectified supplies

Covered syllabus points

21.1 Characteristics of alternating currents21.2 Rectification and smoothing

21. Alternating currents question 1

[Maximum number: 4]

A bridge rectifier contains four diodes. The output of the rectifier is connected to a resistor R, as shown in Fig. 10.1.

Fig. 10.1

Fig. 10.1

The variation with time t of the input e.m.f. E to the rectifier is given by the expression

E=15cos⁡(210t)E=15 \cos (210 t)

where t is measured in seconds and E in volts.
The variation with time t of the potential difference V across resistor R is shown in Fig. 10.2.

Fig. 10.2

Fig. 10.2

Determine:

Question (a)

(a)

the maximum potential difference VMAX V_{\text {MAX }} across resistor R

VMAX⁡=V_{\operatorname{MAX}}=
[ 1 ]

Question (b)

(b)

the time interval, to two significant figures, between time t1t_{1} and time t2t_{2}.
time =
s

[ 3 ]

21. Alternating currents question 2

[Maximum number: 7]

The output potential difference (p.d.) of an alternating power supply is represented by

V=320sin⁡(100πt)V=320 \sin (100 \pi t)

where V is the p.d. in volts and t is the time in seconds.

Question (a)

(a)

Determine the root-mean-square (r.m.s.) p.d. of the power supply.

r.m.s. p.d. =
[ 1 ]

Question (b)

(b)

Determine the period T of the output.

[ 1 ]

Question (c)

(c)

The power supply is connected to resistor R and a diode in the circuit shown in Fig. 10.1.

Fig. 10.1

Fig. 10.1

[ 5 ]

Question (i)

(i)

State the name of the type of rectification produced by the diode in Fig. 10.1.

[ 1 ]

Question (ii)

(ii)

On Fig. 10.2 sketch the variation with time t of the p.d. VRV_{\mathrm{R}} across R from time t=0 to time t=40 mst=40 \mathrm{~ms}.

Fig. 10.2

Fig. 10.2

[ 3 ]

Question (iii)

(iii)

On Fig. 10.1, draw the symbol for a component that may be connected to produce smoothing of VRV_{R}.

[ 1 ]
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