9 practice sets · Page 1 of 1
Which of the following statements is false?
It is cheaper to use a.c. than d.c.
Distribution of a.c. is more convenient than with d.c. since voltages may be readily altered using transformers
An alternator is an a.c. generator
A rectifier changes d.c. to a.c.
The value of an alternating current at any given instant is
a maximum value
a peak value
an instantaneous value
an r.m.s. value
The value normally stated when referring to alternating currents and voltages is the
instantaneous value
r.m.s. value
average value
peak value
The supply of electrical energy for a consumer is usually by a.c. because
transmission and distribution are more easily effected
it is most suitable for variable speed motors
the volt drop in cables is minimal
cable power losses are negligible
The number of complete cycles of an alternating current occurring in one second is known as
the maximum value of the alternating current
the frequency of the alternating current
the peak value of the alternating current
the r.m.s. or effective value
State which of the following is false. For a sine wave
the peak factor is 1.414
the r.m.s. value is 0.707 × peak value
the average value is 0.637 × r.m.s. value
the form factor is 1.11
An alternating voltage of maximum value 100 V is applied to a lamp. Which of the following directvoltages, if applied to the lamp, would cause the lamp to light with the same brilliance?
100 V
63.7 V
70.7 V
141.4 V
An alternating current completes 100 cycles in 0.1 s. Its frequency is
20 Hz
100 Hz
0.002 Hz
1 kHz
An a.c. supply is 70.7 V, 50 Hz. Which of the following statements is false?
The periodic time is 20 ms
The peak value of the voltage is 70.7 V
The r.m.s. value of the voltage is 70.7 V
The peak value of the voltage is 100 V
