CAIE IGCSE Physics 4.2.2.4 Difference between direct current

Practise distinguishing d.c. from a.c. using current or voltage-time graphs, direction changes and labelled circuit supplies.

Exam points

interpret current-time or voltage-time graphs as a.c. or d.c. supplies
describe d.c. as one direction and a.c. as a current that reverses direction
sketch an a.c. current graph with the correct frequency, phase and peak value when given

[Maximum number: 2]

(a)

Describe how a direct current (d.c.) differs from an alternating current (a.c.).

[ 1 ]

(b)

Fig. 9.1 shows how the voltage output of an a.c. generator varies with time.

Fig. 9.1

A heater is connected directly to the a.c. generator and the maximum current in the heater is 0.75 A .

[ 1 ]

(i)

On Fig. 9.2, sketch a graph to indicate how the current in the heater varies with time.

Fig. 9.2

[ 1 ]

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