50 questions · timed · auto-graded
To induce an e.m.f. in a coil, the linking magnetic flux
|
(a) Must decrease |
(b) Can either increase or decrease |
|
(c) Must remain constant |
(d) Must increase |
(b) Can either increase or decrease
A copper ring is held horizontally and a bar magnet is dropped through the ring with its length along the axis of the ring. The acceleration of the falling magnet while it is passing through the ring is
|
(a) Equal to that due to gravity |
|
(b) Less than that due to gravity |
|
(c) More than that due to gravity |
|
(d) Depends on the diameter of the ring and the length of the magnet |
(b) Less than that due to gravity
Assertion : Inductance coil are made of copper.
Reason : Induced current is more in wire having less resistance.
|
(a) If both assertion and reason are true and the reason is the correct explanation of the assertion. |
|
(b) If both assertion and reason are true but reason is not the correct explanation of the assertion. |
|
(c) If assertion is true but reason is false. |
|
(d) If the assertion and reason both are false. |
(a) If both assertion and reason are true and the reason is the correct explanation of the assertion.
Assertion : An aircraft flies along the meridian, the potential at the ends of its wings will be the same.
Reason : Whenever there is change in the magnetic flux e.m.f. induces.
|
(a) If both assertion and reason are true and the reason is the correct explanation of the assertion. |
|
(b) If both assertion and reason are true but reason is not the correct explanation of the assertion. |
|
(c) If assertion is true but reason is false. |
|
(d) If the assertion and reason both are false. |
(a) If both assertion and reason are true and the reason is the correct explanation of the assertion.
Assertion : When two coils are wound on each other, the mutual induction between the coils is maximum.
Reason : Mutual induction does not depend on the orientation of the coils.
|
(a) If both assertion and reason are true and the reason is the correct explanation of the assertion. |
|
(b) If both assertion and reason are true but reason is not the correct explanation of the assertion. |
|
(c) If assertion is true but reason is false. |
|
(d) If the assertion and reason both are false. |
(c) If assertion is true but reason is false.
Assertion : Faraday’s laws are consequences of conservation of energy.
Reason : In a purely resistive ac circuit, the current lags behind the e.m.f. in phase.
|
(a) If both assertion and reason are true and the reason is the correct explanation of the assertion. |
|
(b) If both assertion and reason are true but reason is not the correct explanation of the assertion. |
|
(c) If assertion is true but reason is false. |
|
(d) If the assertion and reason both are false. |
(c) If assertion is true but reason is false.
In an L–R circuit connected to a battery the rate at which energy is stored in the inductor is plotted against time during the growth of the current in the circuit. Which of the following best represents the resulting curve
|
(a)
|
(b)
|
(c)
|
(d)
|
(a)
A conductor of 3 m in length is moving perpendicularly to magnetic field of 
tesla with the speed of 
, then the e.m.f. produced across the ends of conductor will be
|
(a) 0.03 volt |
(b) 0.3 volt |
(c) 3 × |
(d) 3 volt |
(b) 0.3 volt
The resistance in the following circuit is increased at a particular instant. At this instant the value of resistance is 10W. The current in the circuit will be now
|
(a) i = 0.5 A |
(b) i > 0.5 A |
(c) i < 0.5 A |
(d) i = 0 |
(b) i > 0.5 A
A coil having an area 
is placed in a magnetic field which changes from 
to 
in a time interval t. The e.m.f. induced in the coil will be
|
(a) |
(b) |
(c) 
|
(d) 
|
(a) 
A simple pendulum with bob of mass m and conducting wire of length L swings under gravity through an angle 2θ. The earth’s magnetic field component in the direction perpendicular to swing is B. Maximum potential difference induced across the pendulum is
|
(a) 2BL sin |
(b) BL sin |
|
(c) BL sin |
(d) 2BL sin |
(a) 2BL sin
The graph Shows the variation in magnetic flux ∅(t) with time through a coil. Which of the statements given below is not correct
|
(a) There is a change in the direction as well as magnitude of the induced emf between B and D |
|
(b) The magnitude of the induced emf is maximum between B and C |
|
(c)There is a change in the direction as well as magnitude of induced emf between A and C |
|
(d) The induced emf is zero at B |
(d) The induced emf is zero at B
The number of turns in the coil of an ac generator is 5000 and the area of the coil is 
. The coil is rotated at the rate of 100 cycles/sec in a magnetic field of 0.2
. The peak value of the emf generated is nearly
|
(a) 786 kV |
(b) 440 kV |
(c) 220 kV |
(d) 157.1 kV |
(d) 157.1 kV
A coil of 100 turns and area 5 square centimetre is placed in a magnetic field B = 0.2 T. The normal to the plane of the coil makes an angle of 60° with the direction of the magnetic field. The magnetic flux linked with the coil is
|
(a) 5 |
(b) 5 |
(c) |
(d) |
(a) 5 
The dimensions of magnetic flux are
|
(a) |
(b) |
(c) |
(d) |
(d) 
A copper disc of radius 0.1 m is rotated about its centre with 10 revolutions per second in a uniform magnetic field of 0.1 Tesla with its plane perpendicular to the field. The e.m.f. induced across the radius of disc is
|
(a) |
(b) |
(c) π |
(d) 2π |
(c) π 
A small square loop of wire of side l is placed inside a large square loop of wire of side L (L > l). The loop are coplanar and their centre coincide. The mutual inductance of the system is proportional to
|
(a) l / L |
(b) |
(c) L/l |
(d) |
(b) 
When a magnet is pushed in and out of a circular coil C connected to a very sensitive galvanometer G as shown in the adjoining diagram with a frequency v, then
|
(a) Constant deflection is observed in the galvanometer |
|
(b) Visible small oscillations will be observed in the galvanometer if v is about 50 Hz |
|
(c) Oscillations in the deflection will be observed clearly if v = 1 or 2 Hz |
|
(d) No variation in the deflection will be seen if v = 1 or 2 Hz |
(c) Oscillations in the deflection will be observed clearly if v = 1 or 2 Hz
A coil of 40 W resistance has 100 turns and radius 6 mm is connected to ammeter of resistance of 160 ohms. Coil is placed perpendicular to the magnetic field. When coil is taken out of the field, 32 m C charge flows through it. The intensity of magnetic field will be
|
(a) 6.55 T |
(b) 5.66 T |
(c) 0.655 T |
(d) 0.566 T |
(d) 0.566 T
A coil having 500 square loops each of side 10 cm is placed normal to a magnetic flux which increases at the rate of 1.0 tesla/second. The induced e.m.f. in volts is
|
(a) 0.1 |
(b) 0.5 |
(c) 1 |
(d) 5 |
(d) 5
A magnet is brought towards a coil (i) speedly (ii) slowly then the induced e.m.f./induced charge will be respectively
|
(a) More in first case / More in first case |
|
(b) More in first case/Equal in both case |
|
(c) Less in first case/More in second case |
|
(d) Less in first case/Equal in both case |
(b) More in first case/Equal in both case
A rectangular loop is being pulled at a constant speed v, through a region of certain thickness d, in which a uniform magnetic field B is set up. The graph between position x of the right hand edge of the loop and the induced emf E will be
(a)
|
(b)
|
(c)
|
(d)
|
A horizontal loop abcd is moved across the pole pieces of a magnet as shown in fig. with a constant speed v. When the edge ab of the loop enters the pole pieces at time t = 0 sec. Which one of the following graphs represents correctly the induced emf in the coil
(a)
|
(b)
|
(c)
|
(d)
|
A step-up transformer has transformation ratio of 3 : 2. What is the voltage in secondary if voltage in primary is 30 V
| (a) 45 V | (b) 15 V |
(c) 90 V |
(d) 300 V |
(a) 45 V
The magnetic field in a coil of 100 turns and 40 square cm area is increased from 1 Tesla to 6 Tesla in 2 second. The magnetic field is perpendicular to the coil. The e.m.f. generated in it is
|
(a) |
(b) 1.2 V |
(c) 1.0 V |
(d) |
(c) 1.0 V
The direction of induced e.m.f. during electromagnetic induction is given by
|
(a) Faraday's law |
(b) Lenz's law |
(c) Maxwell's law |
(d) Ampere's law |
(b) Lenz's law
Lenz's law is consequence of the law of conservation of
|
(a) Charge |
(b) Momentum |
(c) Mass |
(d) Energy |
(d) Energy
In electromagnetic induction, the induced charge in a coil is independent of
|
(a) Change in the flux |
(b) Time |
|
(c) Resistance in the circuit |
(d) None of the above |
(b) Time
A cylindrical bar magnet is kept along the axis of a circular coil. If the magnet is rotated about its axis, then
|
(a) A current will be induced in a coil |
|
(b) No current will be induced in a coil |
|
(c) Only an e.m.f. will be induced in the coil |
|
(d) An e.m.f. and a current both will be induced in the coil |
(b) No current will be induced in a coil
A circular coil of 500 turns of wire has an enclosed area of 
per turn. It is kept perpendicular to a magnetic field of induction 0.2 T and rotated by 180° about a diameter perpendicular to the field in 0.1 sec. How much charge will pass when the coil is connected to a galvanometer with a combined resistance of 50 ohms
|
(a) 0.2 C |
(b) 0.4 C |
(c) 2 C |
(d) 4 C |
(b) 0.4 C
Assertion : Self-inductance is called the inertia of electricity.
Reason : Self-inductance is the phenomenon, according to which an opposing induced e.m.f. is produced in a coil as a result of change in current or magnetic flux linked in the coil.
|
(a) If both assertion and reason are true and the reason is the correct explanation of the assertion. |
|
(b) If both assertion and reason are true but reason is not the correct explanation of the assertion. |
|
(c) If assertion is true but reason is false. |
|
(d) If the assertion and reason both are false. |
(b) If both assertion and reason are true but reason is not the correct explanation of the assertion.
Assertion : The induced e.m.f. and current will be same in two identical loops of copper and aluminium, when rotated with same speed in the same magnetic field.
Reason : Induced e.m.f. is proportional to rate of change of magnetic field while induced current depends on resistance of wire.
|
(a) If both assertion and reason are true and the reason is the correct explanation of the assertion. |
|
(b) If both assertion and reason are true but reason is not the correct explanation of the assertion. |
|
(c) If assertion is true but reason is false. |
|
(d) If assertion is false but reason is true. |
(d) If assertion is false but reason is true.
Assertion : Magnetic flux can produce induced e.m.f.
Reason : Faraday established induced e.m.f. experimentally.
|
(a) If both assertion and reason are true and the reason is the correct explanation of the assertion. |
|
(b) If both assertion and reason are true but reason is not the correct explanation of the assertion. |
|
(c) If assertion is true but reason is false. |
|
(d) If assertion is false but reason is true. |
(d) If assertion is false but reason is true.
Two identical coaxial circular loops carry current i each circulating in the clockwise direction. If the loops are approaching each other, then
|
(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 |
(c) Current in each loop decreases
Two identical circular loops of metal wire are lying on a table without touching each other. Loop-A carries a current which increases with time. In response, the loop-B
|
(a) Remains stationary |
|
(b) Is attracted by the loop-A |
|
(c) Is repelled by the loop-A |
|
(d) Rotates about its CM, with CM fixed |
(c) Is repelled by the loop-A
If a coil made of conducting wires is rotated between poles pieces of the permanent magnet. The motion will generate a current and this device is called
|
(a) An electric motor |
(b) An electric generator |
|
(c) An electromagnet |
(d) All of above |
(b) An electric generator
In a step up transformer, if ratio of turns of primary to secondary is 1 : 10 and primary voltage is 230 V. If the load current is 2A, then the current in primary is
|
(a) 20 A |
(b) 10 A |
(c) 2 A |
(d) 1 A |
(a) 20 A
A physicist works in a laboratory where the magnetic field is 2 T. She wears a necklace enclosing area 0.01 m2 in such a way that the plane of the necklace is normal to the field and is having a resistance R = 0.01 Ω. Because of power failure, the field decays to 1 T in time 10–3 seconds. Then what is the total heat produced in her necklace ? (T = Tesla)
|
(a) 10 J |
(b) 20 J |
(c) 30 J |
(d) 40 J |
(a) 10 J
A short-circuited coil is placed in a time-varying magnetic field. Electrical power is dissipated due to the current induced in the coil. If the number of turns were to be quadrupled and the wire radius halved, the electrical power dissipated would be
|
(a) Halved |
(b) The same |
(c) Doubled |
(d) Quadrupled |
(b) The same
The induction coil works on the principle of
|
(a) Self-induction |
(b) Mutual induction |
|
(c) Ampere's rule |
(d) Fleming's right hand rule |
(b) Mutual induction
The turn ratio of a transformers is given as 2 : 3. If the current through the primary coil is 3 A, thus calculate the current through load resistance
|
(a) 1 A |
(b) 4.5 A |
(c) 2 A |
(d) 1. 5 A |
(c) 2 A
A step up transformer has transformation ration 5 : 3. What is voltage in secondary if voltage in primary is 60 V
|
(a) 20 V |
(b) 60 V |
(c) 100 V |
(d) 180 V |
(c) 100 V
In a primary coil 5A current is flowing on 220 volts. In the secondary coil 2200V voltage produces. Then ratio of number of turns in secondary coil and primary coil will be
|
(a) 1 : 10 |
(b) 10 : 1 |
(c) 1 : 1 |
(d) 11 : 1 |
(b) 10 : 1
An ideal transformer has 500 and 5000 turn in primary and secondary windings respectively. If the primary voltage is connected to a 6V battery then the secondary voltage is
|
(a) 0 |
(b) 60 V |
(c) 0.6 V |
(d) 6.0 V |
(a) 0
In a transformer, the number of turns in primary coil and secondary coil are 5 and 4 respectively. If 240 V is applied on the primary coil, then the ratio of current in primary and secondary coil is
|
(a) 4 : 5 |
(b) 5 : 4 |
(c) 5 : 9 |
(d) 9 : 5 |
(a) 4 : 5
In an inductor of inductance L = 100 mH, a current of I = 10A is flowing. The energy stored in the inductor is
|
(a) 5 J |
(b) 10 J |
(c) 100 J |
(d) 1000 J |
(a) 5 J
The number of turns in the primary coil of a transformer is 200 and the number of turns in the secondary coil is 10. If 240 volt AC is applied to the primary, the output from the secondary will be
|
(a) 48 V |
(b) 24 V |
(c) 12 V |
(d) 6 V |
(c) 12 V
In a transformer, number of turns in the primary are 140 and that in the secondary are 280. If current in primary is 4A then that in the secondary is
|
(a) 4 A |
(b) 2 A |
(c) 6 A |
(d) 10 A |
(b) 2 A
Large transformers, when used for some time, become hot and are cooled by circulating oil. The heating of transformer is due to
|
(a) Heating effect of current alone |
|
(b) Hysteresis loss alone |
|
(c) Both the hysteresis loss and heating effect of current |
|
(d) None of the above |
(c) Both the hysteresis loss and heating effect of current
A transformer has 100 turns in the primary coil and carries 8 A current. If input power is one kilowatt, the number of turns required in the secondary coil to have 500V output will be
|
(a) 100 |
(b) 200 |
(c) 400 |
(d) 300 |
(c) 400
