An inductor of self inductance 100 mH and a resistor of resistance 50Ω, are connected to a2 V battery.The time required for the current to half its steady value is

2 milli second
2 ln (0.5) milli second
2 ln (3) milli second
2 ln (2) milli second

Solution

The primary of a transformer has 400 turns while the secondary has 2000 turns. If the power output from the secondary at 1000 V is 12 kW, what is the primary voltage?

200 V
300 V
400 V
500 V

Solution

An inductive coil has are sistance of 100 Ω. When an a.c.signal of requency 1000 Hz is fed to the coil, the applied voltage leads the current by 45°. What is the inductance of the coil ?

10 mH
12 mH
16 mH
20 mH

Which of the following statement is incorrect ?

In LCR series ac circuit, as the frequency of the source increases, the impedence 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 impedence of an ac circuit be comespurely resistive.
Below resonance, voltage leads the current while above it, current leads the voltage.

Solution

Option (d) is false because the reason why the voltage leads the current is because ¹⁄_Cω>Lω and if the voltage lags, the inductive reactance is greater than the capacitive reactance.

In the question 86, if the switch is opened after the capacitor has been charged, it will discharges with a time constant

RC
2RC
¹⁄₂ RC
RC ln2

Solution

C discharges through both resistance in series.

In the circuit shown, when the switch is closed, the capacitor charges with a time constant

RC
2RC
¹⁄₂RC
RC ln2

Solution

The resistance in the middle plays no part in the charging process of C, as it does not alter either the potential difference across the RC combination or the current through it.

A steady potential difference of 10 V produces heat at a ratex in a resistor. The peak value of the alternating voltage which will produce heat at a rate ^x⁄₂ in the same resistor is

5 V
5√2 V
10 V
10√2 V

In LCR series circuit fed by a DC source, how does the amplitude of charge oscillations vary with time duringd is charge ?

Two coils A and B are connected in series across a 240 V, 50Hz supply. The resistance of A is 5Ω and the inductance of B is 0.02 H. The power consumed is 3kW and the power factor is 0.75. The impedance of the circuit is