A Level - Alternating Current

Which of the following is/are alternating current(s)?

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UCLES N2006 P1 Q25.

A cathode ray oscilloscope screen with a grid of 1 cm squares displays an alternating voltage waveform. The settings of the oscilloscope are: gain = 0.50 V cm^-1, time base = 5.0 ms cm^-1.

Which of the following gives the expression for the variation of voltage V with respect to time t?

• V =1.0 cos 50 t

• V = 1.0 cos 130 t

• V = 1.0 cos 310 t

• V = 1.0 cos 630 t

UCLES N96/I/21.

An alternating current flows through a resistor.

The variation with time of this current is shown.

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UCLES N93/I/18.

A sinusoidal alternating current of peak value I_o passes through a heater of resistance R.

What is the mean power output of the heater?

The figure shows a graph of the output from an AC voltage source.

What is the average voltage of the AC source?

Give your answer to 3 s.f. in volts and omit the unit when you key in your answer.

The figure shows a graph of the output from an AC voltage source. Determine the root mean square voltage of the AC source.

Give your answer to 3 s.f. in volts and omit the unit when you key in your answer.

An electrical immersion heater is rated "220 V, 800 W, a.c. 50 Hz" (Europe Model). When operating normally, what is the peak current through the heater?

Give your answer to 3 s.f. in amperes and omit units in your final answer.

Modified from CIE J81/II/19.

An alternating current of r.m.s. magnitude 3.0 A and a steady direct current I flowing through identical resistors dissipate heat at equal rates.

What is the value of current I?

• 1.5 A
• 2.1 A
• 3.0 A
• 4.2 A

Modified from CIE J83/I/10b.

The current in a certain circuit varies with time as shown in the figure.

What is the root-mean-square current?

• 1.00 A
• 2.00 A
• 2.83 A
• 4.00 A

CIE J77/II/23.

Half-wave rectification of an alternating sinusoidal voltage of amplitude 200 V gives the waveform shown.

What is the value of r.m.s. value of the rectified voltage?

• 0 V
• 70.7 V
• 100 V
• 14.1 V