The magnetic energy in an inductor changes from maximum value to minimum value in 5 ms when connected to an a.c. source. The frequency of the source is :
50 Hz
200 Hz
500 Hz
20 Hz
A rectangular coil of 20 turns and area of cross-section 25 cm2 has a resistance of 100 Ω. If a magnetic field which is perpendicular to the plane of the coil changes at the rate of 1000 T per second, the current in the coil is
1 A
50 A
0.5 A
5 A
The number of turns in a secondary coil is twice the number of turns in primary. A Leclanche cell of 1.5 V is connected across the primary. The voltage acrosss secondray is
1.5 V
3 V
240 V
zero
A coil of 1000 turns of wire is wound on a book and this book is lying on the table. The vertical component of earth's magnetic field is 0.6 x 10-4 T and the area of the coil is 0.05m2. The book is turned through 180o about a horizontal axis in 0.1 second. The average e.m.f. induced in the coil is :
0.03 V
0.06 V
0.6 V
Two coils have a mutual inductance of 0.005 H. The current changes in the first coil according to the equation I = I0 sin ωt where I0 = 10A and ω = 100π rad/sec. The maximum value of e.m.f. in the second coil is
5π volts
2π volts
π volts
4π volts
Two inductors each of inductance L are connected in parallel. What is their equivalent inductance?
2L
L
L/2
L/4
A long solenoid has 200 turns/cm and carries a current I. The magnetic field at its centre is 5.28 x 10-2 Wbm-2. Another long solenoid has 100 turns/cm and it carries a current I/3. The value of the magnetic field at its centre is
1.05 x 10-2 Wb m-2
1.05 x 10-5 Wb m-2
1.05 x 10-3 Wb m-2
1.05 x 10-4 Wb m-2
A current of 3A flowing in the primary coil is reduced to zero in 0.001s, the induced e.m.f. in the secondary is 15000 V. The mutual inductance between the two coils is
0.5 H
5 H
1.5 H
10 H
A magnet is allowed to fall through a metallic ring. During fall, its acceleration is
less than g
equal to g
greater than g
equal to 2g
A magnetic field of 2 x 10-2 T acts at right angles to a coil of area 100 cm2 with 50 turns. The average e.m.f. induced in the coil is 0.1 V when it is removed from the field in t sec. The value of t is
0.1 s
10 s
0.01 s
1s
