An electric motor operating on a 60 V dc supply draws a current of 10 A. If the efficiency of the motor is 50%, the resistance of its winding is
(1) 3Ω
(2) 6Ω
(3) 15Ω
(4) 30Ω
The potential difference V and the current i flowing through an instrument in an ac circuit of frequency f are given by volts and I = 2 sin ωt amperes (where ω = 2πf). The power dissipated in the instrument is
(1) Zero
(2) 10 W
(3) 5 W
(4) 2.5 W
In an ac circuit, V and I are given by V = 100 sin (100 t) volts, . The power dissipated in circuit is
(1) 104 watt
(2) 10 watt
(3) 2.5 watt
(4) 5 watt
The impedance of a coil, when DC supply is replaced by AC supply:
1. will remain the same
2. will increase
3. will decrease
4. will be zero
A generator produces a voltage that is given by V = 240 sin 120 t, where t is in seconds. The frequency and r.m.s. voltage are
(1) 60 Hz and 240 V
(2) 19 Hz and 120 V
(3) 19 Hz and 170 V
(4) 754 Hz and 70 V
The peak value of an alternating e.m.f. E is given by is 10 volts and its frequency is 50 Hz. At time , the instantaneous e.m.f. is
1. 10 V
2.
3. 5 V
4. 1 V
If a current I given by flows in an ac circuit across which an ac potential of has been applied, then the power consumption P in the circuit will be
(1)
(2)
(3)
(4) P = 0
An alternating current is given by the equation . The r.m.s. current is given by
(1)
(2)
(3)
(4)
A resistance of \(20~ \mathrm{ohms}\) is connected to a source of an alternating potential, \(V=220sin(100 \pi t).\) The time taken by the current to change from its peak value to its r.m.s value will be:
1. | \( 0.2~ \mathrm{sec}\) | 2. | \( 0.25~ \mathrm{sec}\) |
3. | \(25 \times10^{-3}~ \mathrm{sec}\) | 4. | \(2.5 \times10^{-3}~ \mathrm{sec}\) |
Voltage and current in an ac circuit are given by and
(1) Voltage leads the current by 30°
(2) Current leads the voltage by 30°
(3) Current leads the voltage by 60°
(4) Voltage leads the current by 60°