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]
  • a)
    ch-18_qn-120choice_img_no1.png
  • b)
    ch-18_qn-120choice_img_no2.png
  • c)
    ch-18_qn-120choice_img_no3.png
  • d)
    ch-18_qn-120choice_img_no4.png
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]
  • a) 2500 V
  • b) 25,000 V
  • c) 2510 V
  • d) zero
Q.3
The efficiency of transformer is very high because [ MPPMT 1994]
  • a) there is no moving parts in transformer
  • b) it produces very high voltage
  • c) it produces very low voltage
  • 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
  • a) the bulb will light up from an instant when the capacitor starts charging
  • b) the bulb will light up when the capacitor is fully charged
  • c) the bulb will not light up at all
  • 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]
  • a) 5 H
  • b) 10 H
  • c) 11 H
  • 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]
  • a) 200π volt
  • b) 10π/ 3 volt
  • c) 2π/3 volt
  • d) 2/3 volt
Q.7
The device that does not work on the principle of mutual induction us [ CET 1994]
  • a) induction coil
  • b) motor
  • c) tesala coil
  • 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]
  • a) 1.77 volts
  • b) 17.7 volts
  • c) 177 volts
  • d) 0.177 volts
Q.9
The total charge induced in a conductor circuit moving in a magnetic field depends upon .. [ ISM Dhanba 1994]
  • a) the rate of change of magnetic flux linked with it
  • b) the total change of flux through it
  • c) the final magnetic flux
  • 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]
ch-18_que_no-129_img_no1.png
  • a) v > vo
  • b) v < vo
  • c) v = vo
  • d) v = -vo
Q.11
If magnetic mono pole existed which of the following Maxwell's equation would be modified [ AMU 1995]
  • a)
    ch-18_qn-130choice_img_no1.png
  • b)
    ch-18_qn-130choice_img_no2.png
  • c)
    ch-18_qn-130choice_img_no3.png
  • d)
    ch-18_qn-130choice_img_no4.png
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]
  • a) 100A
  • b) 200A
  • c) 22A
  • 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]
  • a) 5.0 coulomb
  • b) 4.0 coulomb
  • c) 1.0 coulomb
  • 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]
  • a) 200v, 50Hz
  • b) 20V, 500Hz
  • c) 2V, 50Hz
  • 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]
  • a) current in each loop increases
  • b) current in each loop remains the same
  • c) current in each loop decreases
  • 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]
  • a) More in case(a)
  • b) Less in case (a)
  • c) same in both the cases
  • 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]
  • a) clockwise
  • b) anticlockwise
  • c) zero
  • d) will depend upon the radius of loop
Q.18
Mutual inductance of two coils can be increased by [ MPPMT 1994]
  • a) Decreasing the number of turns in the coils
  • b) Increasing the number of turns in the coils
  • c) Winding the coils on wooden core
  • 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]
ch-18_que_no-139_img_no1.png
  • a) 3.75×10-3 N
  • b) 3.75×10-2 N
  • c) 3.75×102 N
  • 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]
  • a) 6.25
  • b) 12.5
  • c) 25
  • 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]
  • a) 1
  • b) 5
  • c) 20
  • 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]
  • a) 4.0A/s
  • b) 16.A/s
  • c) 1.6A/s
  • 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]
  • a) 25
  • b) 30
  • c) 35
  • 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]
  • a) 2.5×10-7 weber
  • b) 6.31 ×10-3 weber
  • c) 5.2×10-5 weber
  • d) 4.1×10-5 weber
Q.25
Tick out the wrong statement [ AMU 1995]
  • 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
  • b) The self induced emf produced by changing current in a coil always tends to decrease the current
  • c) Inserting an iron core in a coil increases the coefficient of self-inductance
  • 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]
  • a) L/4
  • b) L
  • c) 4L
  • 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]
  • a) 7 units
  • b) 14 units
  • c) zero units
  • 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]
  • a) 4/√7 A
  • b) 1.0A
  • c) 4/7 A
  • d) 0.8 A
Q.29
The average power dissipation in pure inductance is [ MPPET 1999]
  • a) ½ LI2
  • b) 2LI2
  • c) ¼ LI2
  • d) zero
Q.30
A choke coil has [ Raj.PMT 1997]
  • a) high inductance an high resistance
  • b) low inductance and low resistance
  • c) high inductance and low resistance
  • d) low inductance and high resistance
0 h : 0 m : 1 s