Q.1.
A solenoid has 2000 turns wound over a length of 0.3 m. The area of its cross-section is 1.2×10-3 mAround its central section a coil of 300 turns is wound. If an initial current of 2A is reversed in 0.25 sec, the emf induced in the coil is equal to [ JIMPER Pondy 1998]
-
12%
a) 6.0×10-4 V
-
50%
b) 4.8×10-2V
-
38%
c) 6.0×10-2V
-
0%
d) 48kV
Explanation
Q.2.
The back emf in a DC motor is zero when the [ CPMT 1989]
-
29%
a) motor has picked up maximum speed
-
43%
b) motor has just started moving
-
14%
c) speed of the motor just on the increase
-
14%
d) motor has just switched off
Q.3.
In an inductive circuit the induced emf will be maximum [ Raj.PMT 1996]
-
57%
a) At the time of switching on the resistance
-
0%
b) At the time of switching off the resistance
-
29%
c) At the time of switching off the resistance it will be small
-
14%
d) At the time of switching on the resistance it will be small
Q.4.
The current is passing through a choke coil of self inductance of 0.25H. The rate of change of current is 2amp/sec, then what will be the emf developing across the wire? [ CPMT 1999]
-
0%
a) 500V
-
50%
b) 500 mV
-
50%
c) 50V
-
0%
d) None
Q.5.
The induced emf in a circuit [ CET 1994]
-
0%
a) decreases the magnetic flux through the circuit
-
38%
b) increases the magnetic flux through the circuit
-
38%
c) may increase or decrease the magnetic flux through the circuit
-
25%
d) leaves the magnetic flux through the circuit unchanged
Q.6.
Consider the situation shown in figure. The wire AB is slid on the fixed rails with a constant velocity. IF the wire AB is replaced by a semi-circular wire, the magnitude of the induced current will [ MPPMT 1999]
-
12%
a) Increase
-
62%
b) Remains same
-
12%
c) Decrease
-
12%
d) Increases or decreases depending on whether the semi-circular bulges towards the resistance or away from it
Q.7.
A conducting square loop of side L and resistance R moving in the plane with uniform velocity V perpendicular to one of its sides. A magnetic induction B constant in time and space, pointing perpendicular and into the plane of the loop exists everywhere. the current induced in the loop is [ MPPMT 1999]
-
12%
a) BLV/R clock-wise
-
25%
b) BLV/R anticlock-wise
-
38%
c) 2BLV/R anticlock-wise
-
25%
d) zero
Q.8.
According to Faraday's law of electromagnetic induction:
-
0%
a) The direction of induced current is such that it opposes the cause producing it
-
71%
b) The magnitude of induced emf produced in a coil is directly proportional to the rate of change of magnetic flux
-
14%
c) The direction of induced emf is such that it opposes the cause producing it
-
14%
d) none of above
Q.9.
A cylindrical magnet is placed near a circular coil. The magnet is rotated about its own axis as shown in figure. The induced current in the coil is [ MPT 1995]
-
38%
a) zero
-
12%
b) in anticlock wise direction
-
25%
c) in clock wise direction
-
25%
d) directly proportional to the speed of rotation ω
Q.10.
the armature of DC motor has 20 Ω resistance. It draws current of 1.5 amp when run by 220 V DC supply. The value of back emf induced in it will be [ MPPMT 1999]
-
38%
a) 150V
-
25%
b) 170V
-
25%
c) 180V
-
12%
d) 190V
Q.11.
An inductor may store energy in [ CBSE 1990]
-
0%
a) its electric field
-
14%
b) its coils
-
57%
c) its magnetic field
-
29%
d) both electric and magnetic fields
Q.12.
A square coil of 10-2 square metre area is placed perpendicular to a uniform magnetic field of intensity 103 Weber/metrethe magnetic flux through the coil is [ MPPMT 1990]
-
25%
a) 10 Weber
-
38%
b) 10-5 weber
-
38%
c) 105 weber
-
0%
d) 100 weber
Q.13.
A rectangular coil ABCD is rotated anticlock-wise with a uniform angular velocity about the axis shown in figure. The axis of rotation of the coil as well as the magnetic field B are horizontal. The induced emf in the coil would be maximum when the plane of coil [ CPMT 1988]
-
25%
a) is horizontal
-
38%
b) makes an angle of 45° with the direction of magnetic field
-
25%
c) is at right angles to the magnetic field
-
12%
d) makes an angle of 30° with the magnetic field
Q.14.
In step-up transformer the turn ratio is 1:A Leclanche cell ( emf 1.5V) is connected across the primary. The voltage across secondary is [ MPPMT 1999]
-
0%
a) 3.0 V
-
44%
b) 0.75 V
-
56%
c) Zero
-
0%
d) 1.5 V
Q.15.
The diagram below shows two coils A and B placed parallel to each other at a very small distance. Coil A is connected parallel to an A.C supply. G is a very sensitive galvanometer. When the key is closed [ CPMT 1986]
-
29%
a) constant deflection will be observed in galvanometer for a 50 Hz supply
-
14%
b) visible small variation will be observed in the galvanometer for 50Hz input
-
43%
c) Oscillations in the galvanometer may be observed when the input a.c. voltage has a frequency of 1 to 2 HZ
-
14%
d) No variation will be observed in galvanometer even when the input a.c. Voltage is 1 or 2Hz
Q.16.
A square shaped coil of side 10cm and number of turns 500 is placed perpendicular to magnetic flux lines, which is changing at the rate of 1.0 tesla/sec. The emf induced in the coil is [ CPMT 1990]
-
0%
a) 0.1V
-
71%
b) 0.5V
-
14%
c) 1.0V
-
14%
d) 5.0V
Q.17.
transformer is used to [ MPPMT 1999]
-
25%
a) Change the alternating potential
-
25%
b) Change the alternating current
-
25%
c) To prevent the power loss in alternating current flow
-
25%
d) To increase the power of current source
Q.18.
If current increases from zero to one ampere in 0.1 second in coil of 5mH, then the magnitude of the induced emf will be [ MPPMT 1988]
-
0%
a) 0.005V
-
75%
b) 0.05V
-
12%
c) 0.5V
-
12%
d) 5.0V
Q.19.
When a wire loop is rotated in a magnetic field, the direction of induced emf changes once in each [ MPPET 1993]
-
25%
a) (1/4) revolution
-
50%
b) (1/2) revolution
-
12%
c) 1 revolution
-
12%
d) 2 revolution
Q.20.
An area A (=0.5 m2) shown in the figure is situated in a uniform magnetic field B = 4.0 wb/ m2 and makes angle of 60° with the field. The magnetic flux passing through the area A would be [ MPPMT 1999]
-
25%
a) 2 weber
-
25%
b) 1.0 weber
-
38%
c) √3 weber
-
12%
d) 0.5 weber
Q.21.
What is the coefficient of mutual inductance, when the magnetic flux changes by 2×10-2 Wb, and change in current is 0.01A? [BHU 1998]
-
25%
a) 2 henry
-
25%
b) 3 henry
-
12%
c) 1/2 henry
-
38%
d) zero
Q.22.
Quantity that remains unchanged in a transformer is [ MPPMT 1998]
-
0%
a) Voltage
-
67%
b) frequency
-
17%
c) current
-
17%
d) none of these
Q.23.
An inductor coil of inductance L is divided into two equal parts and both parts are connected in parallel. The net inductance is [ BHU 1998]
-
10%
a) L
-
30%
b) 2L
-
20%
c) L/2
-
40%
d) L/4
Explanation
Q.24.
If the rotational velocity of dynamo armature is doubled, then the induced emf will [ MPPMT 1995]
-
12%
a) become half
-
62%
b) become double
-
12%
c) become quadruple
-
12%
d) remains unchanged
Q.25.
Two coils X and Y are placed in a circuit such that a current changes by 2amp in coil X and the magnetic flux change of 0.4 weber occurs in Y. The value of mutual inductance of coil with its unit is [ MPPMT 1990]
-
62%
a) 0.2 henry
-
38%
b) 5 henry
-
0%
c) 0.2 weber
-
0%
d) 0.8 henry
Q.26.
If the angular speed of rotation of an armature of alternating current generator is doubled, then the induced electromotive force will be [ MPPMT 1998]
-
50%
a) Twice
-
25%
b) Four times
-
25%
c) No change
-
0%
d) Half
Q.27.
A step-up transformer has transformation ratio of 3:What is the volatge in secondary, if voltage in primary is 30V? [ BHU 1998]
-
12%
a) 45 V
-
12%
b) 15 V
-
38%
c) 90 V
-
38%
d) 300 V
Q.28.
THe direction of induced current is such that it opposes the very cause that has produced it. This is the law of: [MPPMT 1998]
-
71%
a) Lenz
-
0%
b) Faraday
-
14%
c) Kirchhoff
-
14%
d) Fleming
Q.29.
A low-loss transformer has 230 volts applied to the primary and gives 4.6 volts in the secondary. Secondary is connected to a load which draws 5 amp. of current. The current ( in amp.) in the primary is [ SCRA 1994]
-
50%
a) 0.1
-
25%
b) 1.0
-
0%
c) 10
-
25%
d) 250
Q.30.
Two coils have a mutual inductance 0.005H. The current changes in the first coil according to equation I = Iosinωt, where Io = 10A and ω = 100π radian / second. The maximum value of emf in the second coil is [ CBSE 1998]
-
0%
a) 2π
-
50%
b) 5π
-
25%
c) π
-
25%
d) 4π
Explanation
