CBSE
Multiple Choice QuestionsThe core used in transformer and other electromagnetic instruments is laminated, the reason is
to increase the electric field
to increase the magnetic field
to reduce the loss of energy due to eddy currents
to decrease the resistance
Power factor of L-C-R circuit in resonation condition is
1
zero
A sinusoidal voltage of peak value 300 V and an angular frequency = 400 rad/s is applied to series L-C-R circuit, in which R = 3 , L = 20 mH and C = 625 µF. The peak current in the circuit is
30 A
60 A
100 A
60 A
A step-up transformer has transformation ratio 3 : 2. The voltage in the secondary coil, if the voltage in the primary is 30 V will be
300 V
90 V
45 V
23 V
An L-C-R series circuit consists of a resistance of 10 Ω a capacitor of reactance 6.0 Ω and an inductor coil. The circuit is found to resonate when put across a 300 V, 100 Hz supply. The inductance of coil is (take = 3)
0.1 H
0.01 H
0.2 H
0.02 H
In L-R circuit the current increases to three - fourth of its maximum value in 4s, then the time constant of the circuit is
2 loge 2
A circuit contains a capacitor and inductance each with negligible resistance. The capacitor is initially charged and the charging battery is disconnected. At subsequent time, the charge on the capacitor will
increase exponentially
decrease exponentially
decrease linearly
remain constant
An inductor and a capacitor are connected in an AC circuit inductance and capacitance are 1 H and 25 µF, then for maximum current, angular frequency will be (circuit is connected in series)
200 rad/s
50 rad/s
100 rad/s
150 rad/s
A transformer of 100% efficiency has 200 turns in the primary and 40000 turns in secondary. It is connected to a 220 V main supply and secondary feeds to a 100 kresistance. The potential difference per turn is
1.1 V
25 V
18 V
11 V
A metal wire of linear mass density of 9.8 g/m is stretched with a tension of 10 kg-wt between two rigid supports 1m apart. The wire passes at its middle point between the poles of a permanent magnet and it vibrates in resonance when carrying an alternating current of frequency η. The frequency η of the alternating source is
50 Hz
100 Hz
200 Hz
25 Hz
