Q.1.
The number of turns in the primary and the secondary of a transformer are Np and Ns respectively. The resistance of the secondary circuit is Rs. From the point of view of the primary circuit, the equivalent resistance of the load is [ MPPMT 1997]
-
0%
a)
-
71%
b)
-
14%
c)
-
14%
d)
Explanation
Q.2.
The self-inductance of an induction coil is 5H. If the current in the primary changes from 5 A to zero in 10-3 sec time, the induced emf in the secondary coil will be [ Raj.PET 1996]
-
50%
a) 2500 V
-
12%
b) 25,000 V
-
25%
c) 2510 V
-
12%
d) zero
Q.3.
The efficiency of transformer is very high because [ MPPMT 1994]
-
50%
a) there is no moving parts in transformer
-
25%
b) it produces very high voltage
-
12%
c) it produces very low voltage
-
12%
d) none of the above
Q.4.
A light bulb, a capacitor and battery are connected together. When the switch is closed, which of the following is true
-
67%
a) the bulb will light up from an instant when the capacitor starts charging
-
11%
b) the bulb will light up when the capacitor is fully charged
-
0%
c) the bulb will not light up at all
-
22%
d) the bulb will light up and go off at regular intervals
Q.5.
A varying current in a coil changes from 10 amp to zero in 0.5 sec. If the average emf induced in the coil is 220 volts, the self inductance of coil is [ EAMCET 19994]
-
22%
a) 5 H
-
56%
b) 10 H
-
22%
c) 11 H
-
0%
d) 12 H
Q.6.
A coil of area 80 square cm and 50 turns is rotating with 2,000 revolutions per minute about an axis perpendicular to a magnetic field of 0.05 tesla. The maximum value of the emf developed in it is [ MPPMT 1994]
-
25%
a) 200π volt
-
25%
b) 10π/ 3 volt
-
38%
c) 2π/3 volt
-
12%
d) 2/3 volt
Q.7.
The device that does not work on the principle of mutual induction us [ CET 1994]
-
0%
a) induction coil
-
43%
b) motor
-
43%
c) tesala coil
-
14%
d) transformer
Q.8.
A 50 turn circular coil has a radius of 3cm it is kept in a magnetic field acting normal to the area of the coil. The magnetic field B is increased from 0.1 tesla to 0.35 tesla in 2 milli-seconds. The average induced emf in the coil is [ MPPMT 1994]
-
50%
a) 1.77 volts
-
33%
b) 17.7 volts
-
0%
c) 177 volts
-
17%
d) 0.177 volts
Q.9.
The total charge induced in a conductor circuit moving in a magnetic field depends upon .. [ ISM Dhanba 1994]
-
29%
a) the rate of change of magnetic flux linked with it
-
43%
b) the total change of flux through it
-
0%
c) the final magnetic flux
-
29%
d) the number of lines of force initially linked with the circuit
Q.10.
Two long parallel metallic wires with a resistance R form a horizontal plane. A conducting rod AB is on the wire as shown here. The space has a magnetic field pointing vertically upwards. The rod is given an initial velocity vo. There is no friction and no resistance in the wires and the rod. After a time t the velocity of the rod will be v such that [ PMT 1995]
-
25%
a) v > vo
-
50%
b) v < vo
-
25%
c) v = vo
-
0%
d) v = -vo
Q.11.
If magnetic mono pole existed which of the following Maxwell's equation would be modified [ AMU 1995]
-
17%
a)
-
33%
b)
-
17%
c)
-
33%
d)
Q.12.
A transformer connected to 220 volt line shows an out put of 2A at 11000 volt. The efficiency is 100%. The current drawn from the line is [ PMT 1995]
-
56%
a) 100A
-
22%
b) 200A
-
0%
c) 22A
-
22%
d) 11A
Q.13.
In a circuit with a coil of resistance 2Ω the magnetic flux changes from 2Wb to 10.0 Wb in 0.2 second. The charge that flows in the coil during this time is [ MPPMT 1997]
-
25%
a) 5.0 coulomb
-
38%
b) 4.0 coulomb
-
12%
c) 1.0 coulomb
-
25%
d) 0.8 coulomb
Q.14.
The primary winding of a transformer has 500 turns where as its secondary has 500 turns. The primary is connected to an a.c supply of 20V, 50Hz. The secondary will have an output of [ CBSE 1997]
-
50%
a) 200v, 50Hz
-
0%
b) 20V, 500Hz
-
38%
c) 2V, 50Hz
-
12%
d) 2V, 5Hz
Q.15.
Two identical coaxial circular loops carry current I each circulating in the clockwise direction. If the loops are approaching each other, then [ PMT 1995]
-
43%
a) current in each loop increases
-
0%
b) current in each loop remains the same
-
0%
c) current in each loop decreases
-
57%
d) current in one loop increases and in the other it decreases
Q.16.
A magnet is brought near a ring a) quickly b) slowly, induced emf will be [ Raj.PMT 1997]
-
43%
a) More in case(a)
-
29%
b) Less in case (a)
-
14%
c) same in both the cases
-
14%
d) Depends on the radius of ring
Q.17.
Two loops of different wires are placed concentrically in a plane. If the current in the outer loop is made to pass clockwise and current increases with time, the induced current in the inner loop will be [ Rj.PET 1996]
-
29%
a) clockwise
-
57%
b) anticlockwise
-
14%
c) zero
-
0%
d) will depend upon the radius of loop
Q.18.
Mutual inductance of two coils can be increased by [ MPPMT 1994]
-
0%
a) Decreasing the number of turns in the coils
-
86%
b) Increasing the number of turns in the coils
-
0%
c) Winding the coils on wooden core
-
14%
d) None of above
Q.19.
As shown in figure a metal rod of length 50cm makes contact and complete the circuit. The circuit is perpendicular to the magnetic field with B = 0.15 tesla. If the resistance is 3Ω, force needed to move the rod as indicated with a constant speed of 2m/s is : [ MPPMT 1994]
-
29%
a) 3.75×10-3 N
-
29%
b) 3.75×10-2 N
-
0%
c) 3.75×102 N
-
43%
d) 3.75×10-4 N
Q.20.
The number of turns of primary and secondary coils of a transformer are 5 and 10, respectively and the mutual inductance of the transformer is 25henry. Now the number of turns in the primary and secondary of the transformer are made 10 and 5 respectively. the mutual inductance of the transformer in Henry will be [ MPPET 1995]
-
29%
a) 6.25
-
29%
b) 12.5
-
43%
c) 25
-
0%
d) 50
Q.21.
When current in a coil changes to 2 amp from 8 amper in 3×10-3 second, the emf induced in the coil is 2 volt. The self-inductance of the coil in millihenry is [ MPPMT 1995]
-
12%
a) 1
-
25%
b) 5
-
12%
c) 20
-
50%
d) 10
Q.22.
The mutual inductance between a primary and secondary circuit is 0.5H. The resistance of the primary and the secondary circuit are 20Ω and 5Ω respectively. To generate a current of 0.4A in the secondary, the current in the primary must be changed at the rate of [ MPPMT 1997]
-
14%
a) 4.0A/s
-
57%
b) 16.A/s
-
0%
c) 1.6A/s
-
29%
d) 8.0A/s
Q.23.
The secondary of transformer gives 200 volts when 2.0 kilowatt power is suppled to its 500 turn primary at 0.5 ampere. The number of turns in the secondary is [ AMU 1995]
-
14%
a) 25
-
0%
b) 30
-
57%
c) 35
-
29%
d) 40
Q.24.
A solenoid is 1.5 m long and its inner diameter is 4.0 cm. It has three layers of windings of 1000 turns each and carries a current of 2.0 amperes. The magnetic flux for a cross-section of the solenoid is nearly [ AMU 1995]
-
14%
a) 2.5×10-7 weber
-
29%
b) 6.31 ×10-3 weber
-
43%
c) 5.2×10-5 weber
-
14%
d) 4.1×10-5 weber
Q.25.
Tick out the wrong statement [ AMU 1995]
-
57%
a) An emf can be inducted between the ends of a straight conductor by moving the ends of a straight conductor by moving it through a uniform magnetic field
-
14%
b) The self induced emf produced by changing current in a coil always tends to decrease the current
-
14%
c) Inserting an iron core in a coil increases the coefficient of self-inductance
-
14%
d) According to lenz's law, direction of the induced current is such that it opposes the flux change that causes it
Q.26.
The self-inductance of a coil is L. Keeping the length and area same, the number of turns in the coil is increased to four times. the self inductance of the coil will now be [ MPPMT 1997]
-
14%
a) L/4
-
0%
b) L
-
43%
c) 4L
-
43%
d) 16L
Q.27.
A galvanometer is connected to the secondary coil. The galvanometer shows an instantaneous deflection of 7 division when current is started in primary coil of solenoid. Now if primary coil is suddenly rotated through 180°, then the new instantaneous deflection will be [ CPMT 1991]
-
25%
a) 7 units
-
50%
b) 14 units
-
25%
c) zero units
-
0%
d) 21 units
Q.28.
An emf E = 4cos(1000 t) volt is applied to an LR-circuit of inductance 3mH and resistance 4Ω. The amplitude of current in the circuit is [ MPPMT 1997]
-
12%
a) 4/√7 A
-
12%
b) 1.0A
-
62%
c) 4/7 A
-
12%
d) 0.8 A
Q.29.
The average power dissipation in pure inductance is [ MPPET 1999]
-
50%
a) ½ LI2
-
25%
b) 2LI2
-
12%
c) ¼ LI2
-
12%
d) zero
Q.30.
A choke coil has [ Raj.PMT 1997]
-
0%
a) high inductance an high resistance
-
0%
b) low inductance and low resistance
-
50%
c) high inductance and low resistance
-
50%
d) low inductance and high resistance