WorksheetsA Level - Alternating Current
Total questions: 14
Worksheet time: 21mins
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.
UCLES N93/I/18.
A sinusoidal alternating current of peak value Io passes through a heater of resistance R.
What is the mean power output of the heater?
2Io2R
2Io2R
Io2R
Io2R2
2Io2R
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.
(a)
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.
(a)
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.
(a)
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?
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?
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?
Electrical power P from a substation is to be transmitted at a voltage V via a long cable to a factory.
Which of the following statements is correct when we increase the voltage of transmission?
What quantity is constant when the transmission voltage is increased?
Choose the correct statements.
Power loss is given by P=RV2 , a larger V will imply a greater power is lost.
Power loss will be less, because when we increase the voltage of transmission, there will be a smaller current through the cables, resulting in less power dissipated through joule heating in the wire.
Power loss will be bigger because if we increase the voltage of transmission, a greater current is through the cables P=I2R , hence a larger current will imply a greater loss
UCLES N78/II/22; CIE J84/II/24.
In an ideal transformer, the most important function of the soft-iron core is
UCLES N2007/I/33.
A 100% efficient transformer is connected as shown to a sinusoidal a.c. supply. What is the reading on the ammeter?
UCLES N91/I/21; CIE J95/I/20.
The diagram shows a circuit used to rectify an alternating current. A cathode-ray oscilloscope (c.r.o.) with fixed settings of time-base and Y-gain is connected in turn as shown and produces a trace on c.r.o.
Which diagram shows the trace most accurately?
