A transformer of efficiency 90% draws an input power of 4 kW. An electrical appliance connected across the secondary draws a current of 6 A. The impedance of the device is
60 Ω
50 Ω
80 Ω
100 Ω
The resonance frequency of the tank circuit of an oscillator when and C = 0.04 µF are connected in parallel is
250 kHz
25 kHz
2.5 kHz
25 MHz
An alternating voltage e = 200 sin 100 t is applied to a series combination R = 30 Ω and an inductor of 400 mH. The power factor of the circuit is
0.01
0.2
0.6
0.042
A transformer has an efficiency of 80%. It is connected to a power input of 5 kW at 200 V. If the secondary voltage is 250 V, the primary and secondary currents are respectively
25 A, 20 A
20 A, 16 A
25 A, 16 A
40 A, 25 A
When a DC voltage of 200 V is applied to a coil of self-inductance H, a current of 1 A flows through it. But by replacing DC source with AC source of 200 V, the current in the coil is reduced to 0.5 A. Then the frequency of AC supply is
100 Hz
75 Hz
50 Hz
30 Hz
In a L-R circuit, the value of L is and the value of R is 30 Ω. If in the circuit, an alternating emf of 200 V at 30 cycles/s is connected, the impedance of the circuit and current will be
11.4 Ω, 17.5 A
30.7 Ω, 6.5 A
40.4 Ω, 5 A
50 Ω, 4 A
Which ofthe following statement is incorrect ?
In LCR series AC circuit, as the frequency of the source increases, the impedance of the circuit first decreases and then increases
If the net reactance of an LCR series AC circuit is same as its resistance, then the current lags behind the voltage by 45°
At resonance, the impedance of an AC circuit becomes purely resistive
At resonance in LCR series AC circuit, the potential drops across inductor and capacitor are equal m magnitude but opposite in sign
If an alternating voltage is represented as E = 141 sin (628 t), then the rms value of the voltage and the frequency are respectively
141 V, 628 Hz
100 V, 50 Hz
100 V, 100 Hz
141 V, 100 Hz
A step-down transformer is used on a 1000 V line to deliver 20 A at 120 V at the secondary coil. If the efficiency of the transformer is 80%, the current drawn from the line is
3 A
30 A
0.3 A
2.4 A
For the series LCR circuit shown in the figure, what is the resonance frequency and the amplitude of the current at the resonating frequency ?
2500 rad s-1 and
2500 rad s-1 and 5 A
2500 rad s-1 and
250 rad s-1 and