  Previous Year Questions

## Electromagnetic Induction

- It's good to be already prepared. Go through the previous year questions.
1
A long solenoid of radius carries a time (t)-dependent current . A ring of radius is placed coaxially near its middle. During the time interval , the induced current and the induced in the ring change as:
A
At direction of reverses and is zero.
B
Direction if remains unchanged and is zero at
C
At direction of reverses and is maximum.
D
Direction of remains unchanged and is maximum at
A conducting circular loop made of a thin wire, has area and resistance . It is placed perpendicular to a time dependent magnetic field . The field is uniform in space. Then the net charge flowing through the loop during and is close to:
A
B
C
D
The figure shows a square loop of side which is connected to a network of resistances. The whole setup is moving towards right with a constant speed of . At some instant, a part of L is in a uniform magnetic field of , perpendicular to the plane of the loop. If the resistance of is , the current in the loop at that instant will be close to :
A
B
C
D
A power transmission line feeds input power at to a step down transformer with its primary windings having turns, giving the output power at . If the current in the primary of the transformer is , and its efficiency is , the output current would be:
A
B
C
D
A coil of cross-sectional area having turns is placed in a uniform magnetic field . When it is rotated with an angular velocity , the maximum e.m.f. induced in the coil will be
A
B
C
D
A small circle loop of wire of radius a is located at the centre of a much larger circular wire loop of radius . The two loops are in the same plane. The outer loop of radius carries an alternating current . The emf induced in the smaller inner loop is nearly :
A
B
C
D
Consider a thin metallic sheet perpendicular to the plane of the paper moving with speed in a uniform magnetic field B going into the plane of the paper (See figure). If charge densities and are induced on the left and right surfaces, respectively, of the sheet then (ignore fringe effects) :
A
B
C
D
A fighter plane of length 20 m, wing span (distance from tip of one wing to the tip of the other wing) of 15 m and height 5 m is flying towards east over Delhi. Its speed is . The earth's magnetic field over Delhi is T with the declination angle and dip of such that . If the voltage developed is between the lower and upper side of the plane and between the tips of the wings then and are close to
A
with left side of pilot at higher voltage
B
with right side of pilot at higher voltage
C
with right side of pilot at high voltage
D
with left side of pilot at higher voltage
A conducting metal circular-wire-loop of radius r is placed perpendicular to a magnetic field which varies with time as , where and  are constants, at time t = 0. If the resistance of the loop is R then the heat generated in the loop after a long time is
A
B
C
D
2
A light disc made of aluminium (a nonmagnetic material) is kept horizontally and is free to rotate about its axis as shown in the figure. A strong magnet is held vertically at a point above the disc away from its axis. On revolving the magnet about the axis of the disc, the disc will (figure is schematic and not drawn to scale)
A
rotate in the direction opposite to the direction of magnets motion
B
rotate in the same direction as the direction of magnets motion
C
not rotate and its temperature will remain unchanged
D
not rotate but its temperature will slowly rise
The inductors of two LR circuits are placed next to each other, as shown in the figure. The values of the self-inductance of the inductors, resistances, mutual-inductance and applied voltages are specified in the given circuit. After both the switches are closed simultaneously, the total work done by the batteries against the induced EMF in the inductors by the time the currents reach their steady state values is ______ mJ.
A conducting wire of parabolic shape, , is moving with velocity in a non-uniform magnetic field , as shown in figure. If , , L and are positive constants and is the potential difference developed between the ends of the wire, then the correct statement(s) is/are?
This question has multiple correct options
A
for
B
remains same if the parabolic wire is replaced by a straight wire, , initially, of length
C
for
D
is proportional to the length of wire projected on y-axis
A cm long perfectly conducting wire PQ is moving with a velocity 1 cm/s on a pair of horizontal rails of zero resistance. One side of the rails is connected to an inductor mH and a resistance as shown in figure. The horizontal rail, L and R lie in the same plane with a uniform magnetic field perpendicular to the plane. If the key S is closed at certain instant , the current in the circuit after 1 millisecond is , where the value of x is ____ .
[Assume  the velocity of wire PQ remains constant (1 cm/s) after key S is closed. Given : , where e is base of the natural logarithm]
A circular insulated copper wire loop is twisted to form two loops of area and as shown in the figure. At the point of crossing the wires remain electrically insulated from each other. The entire loop lies in the plane (of the paper). A uniform magnetic field  point into the plane of the paper. At , the loop starts rotating about the common diameter as axis with a constant angular velocity in the magnetic field. Which of the following options is/are correct?
This question has multiple correct options
A
The amplitude of the maximum net induced due to both the loops is equal to the amplitude of maximum induced in the smaller loop alone
B
The rate of change of the flux is maximum when the plane of the loops is perpendicular to plane of the paper
C
The induced in the loop is proportional to the sum of the areas of the two loops
D
The net induced due to both the loops is proportional to
A conducting loop in the shape of a right angled isosceles triangle of height cm is kept such that the vertex is very close to an infinitely long conducting wire (see the figure). The wire is electrically insulated from the loop. The hypotenuse of the triangle is parallel to the wire. The current in the triangular loop is in counter clockwise direction and increased at a constant rate of 10 . Which of the following statement (s) is (are) true?
This question has multiple correct options
A
There is a repulsive force between the wire and the loop
B
If the loop is rotated at a constant angular speed about the wire, an additional emf of volt is induced in the wire
C
The magnitude of induced emf in the wire is volt
D
The induced current in the wire is in opposite direction to the current along the hypotenuse
A rigid wire loop of square shape having side of length L and resistance R is moving along the x-axis with a constant velocity  in the plane of the paper. At t=0, the right edge of the loop enters a region of length 3L where there is a uniform magnetic field  into the plane of the paper, as shown in the figure. For sufficient large , the loop eventually crosses the region. Let x be the location of the right edge of the loop. Let  and  represent the velocity of the loop, current in the loop, and force on the loop, respectively, as a function of x. Counter-clockwise current is taken as positive.
Which of the following schematic plot(s) is (are) correct? (Ignore gravity)
This question has multiple correct options
A
B
C
D