Q.1
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]
ch-18_que_no-64_img_no1.png
  • a) Increase
  • b) Remains same
  • c) Decrease
  • d) Increases or decreases depending on whether the semi-circular bulges towards the resistance or away from it
Q.2
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]
ch-18_que_no-65_img_no1.png
  • a) BLV/R clock-wise
  • b) BLV/R anticlock-wise
  • c) 2BLV/R anticlock-wise
  • d) zero
Q.3
According to Faraday's law of electromagnetic induction:
  • a) The direction of induced current is such that it opposes the cause producing it
  • b) The magnitude of induced emf produced in a coil is directly proportional to the rate of change of magnetic flux
  • c) The direction of induced emf is such that it opposes the cause producing it
  • d) none of above
Q.4
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]
ch-18_que_no-67_img_no1.png
  • a) zero
  • b) in anticlock wise direction
  • c) in clock wise direction
  • d) directly proportional to the speed of rotation ω
Q.5
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]
  • a) 150V
  • b) 170V
  • c) 180V
  • d) 190V
Q.6
An inductor may store energy in [ CBSE 1990]
  • a) its electric field
  • b) its coils
  • c) its magnetic field
  • d) both electric and magnetic fields
Q.7
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]
ch-18_que_no-71_img_no1.png
  • a) is horizontal
  • b) makes an angle of 45° with the direction of magnetic field
  • c) is at right angles to the magnetic field
  • d) makes an angle of 30° with the magnetic field
Q.8
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]
  • a) 3.0 V
  • b) 0.75 V
  • c) Zero
  • d) 1.5 V
Q.9
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]
ch-18_que_no-73_img_no1.png
  • a) constant deflection will be observed in galvanometer for a 50 Hz supply
  • b) visible small variation will be observed in the galvanometer for 50Hz input
  • c) Oscillations in the galvanometer may be observed when the input a.c. voltage has a frequency of 1 to 2 HZ
  • d) No variation will be observed in galvanometer even when the input a.c. Voltage is 1 or 2Hz
Q.10
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]
  • a) 0.1V
  • b) 0.5V
  • c) 1.0V
  • d) 5.0V
Q.11
transformer is used to [ MPPMT 1999]
  • a) Change the alternating potential
  • b) Change the alternating current
  • c) To prevent the power loss in alternating current flow
  • d) To increase the power of current source
Q.12
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]
  • a) 0.005V
  • b) 0.05V
  • c) 0.5V
  • d) 5.0V
Q.13
When a wire loop is rotated in a magnetic field, the direction of induced emf changes once in each [ MPPET 1993]
  • a) (1/4) revolution
  • b) (1/2) revolution
  • c) 1 revolution
  • d) 2 revolution
Q.14
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]
ch-18_que_no-80_img_no1.png
  • a) 2 weber
  • b) 1.0 weber
  • c) √3 weber
  • d) 0.5 weber
Q.15
Quantity that remains unchanged in a transformer is [ MPPMT 1998]
  • a) Voltage
  • b) frequency
  • c) current
  • d) none of these
Q.16
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]
  • a) L
  • b) 2L
  • c) L/2
  • d) L/4
Q.17
If the rotational velocity of dynamo armature is doubled, then the induced emf will [ MPPMT 1995]
  • a) become half
  • b) become double
  • c) become quadruple
  • d) remains unchanged
Q.18
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]
  • a) 0.2 henry
  • b) 5 henry
  • c) 0.2 weber
  • d) 0.8 henry
Q.19
If the angular speed of rotation of an armature of alternating current generator is doubled, then the induced electromotive force will be [ MPPMT 1998]
  • a) Twice
  • b) Four times
  • c) No change
  • d) Half
Q.20
A step-up transformer has transformation ratio of 3:What is the volatge in secondary, if voltage in primary is 30V? [ BHU 1998]
  • a) 45 V
  • b) 15 V
  • c) 90 V
  • d) 300 V
Q.21
THe direction of induced current is such that it opposes the very cause that has produced it. This is the law of: [MPPMT 1998]
  • a) Lenz
  • b) Faraday
  • c) Kirchhoff
  • d) Fleming
Q.22
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]
  • a) 0.1
  • b) 1.0
  • c) 10
  • d) 250
Q.23
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]
  • a) 2π
  • b) 5π
  • c) π
  • d) 4π
Q.24
A step-up transformer operates on a 230 volt line and supplies to the load 2amp. The ratio of primary and secondary winding is 1:Determine the primary current [ JIMPER 1998]
  • a) 12.5 amp
  • b) 50 amp
  • c) 8.8 amp
  • d) 25.0 amp
Q.25
Self inductance of solenoid is [ MPPMT 1993]
  • a) Directly proportional to current flowing through coil
  • b) Directly proportional to the length
  • c) Directly proportional to its area of cross-section
  • d) Inversely proportional to the area of cross section
Q.26
The current passing through a chock coil of 5 henry is decreasing at the rate of 2 amp/sec. The emf developed across the coil is [ MPPMT 1990]
  • a) -2.5 volt
  • b) -10.0 volt
  • c) +10 volt
  • d) +2.5 volt
Q.27
A coil of 40Ω resistance has 100 turns and radius 6mm is connected to ammeter of resistance of 160Ω. Coil is placed perpendicular to the magnetic field. When coil is taken out of the field, 32µC charge flows through it. The intensity of magnetic field will be [ Raj.PET 1997]
  • a) 6.55 T
  • b) 5.66T
  • c) 0.655 T
  • d) 0.566T
Q.28
A transformer is employed to [ MPPMT 1988]
  • a) obtain a suitable D.C voltage
  • b) Convert D.D into A.C
  • c) Obtain a suitable A.C. voltage
  • d) convert A.C. into D.C
Q.29
A coil of area 100cm2 has 500 turns. Magnetic field of 0.1 weber/m2 is perpendicular to the coil. The field is reduced to zero in 0.1 second. The induced emf in the coil is [ MPPMT 1991]
  • a) 1 volt
  • b) 5 volts
  • c) 50 volts
  • d) zero
Q.30
The armature current in a D.C. motor is maximum when [ PMT 1986]
  • a) the motor has picked up maximum speed
  • b) the motor has just started moving
  • c) the motor has intermediate speed
  • d) the motor has just been switched off
0 h : 0 m : 1 s