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Recent questions in Electromagnetic induction

Questions >> CBSE XII >> Physics >> Electromagnetic induction

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asked Jul 10, 2017 by pady_1

1 answer

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asked Jul 10, 2017 by pady_1

1 answer

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asked Jul 10, 2017 by pady_1

1 answer

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asked Jul 10, 2017 by pady_1

1 answer

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asked Jul 5, 2017 by pady_1

1 answer

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asked Jul 5, 2017 by pady_1

1 answer

ODBAC is a fixed rectangular conductor of negligible resistance (co is not connected) and OP is a conductor which rotates clockwise with an angular velocity $w$ as shown in the fig. The entire system is in a uniform magnetic field B whose direction is along the normal to the surface of the rectangular conductor ABDC. The conductor OP is in electric contact with ABDC. The rotating conductor has resistance of X per unit length. Find the current in the rotating conductor as it rotates by $180^{\circ}$

asked Jan 1, 2017 by priyanka.c

1 answer

A conducting wire XY of mass $m$ and negligible resistance slides smoothly on two parallel conducting wire as shown in the fig. The closed circuit has a resistance R due to AC. AB and CD are perfect conductors. There is a magnetic field $B = B (+) \hat {k}$ . Is there a decrease in kinetic energy of XY equalling the heat lost in R ?

asked Jan 1, 2017 by priyanka.c

1 answer

A conducting wire XY of mass $m$ and negligible resistance slides smoothly on two parallel conducting wire as shown in the fig. The closed circuit has a resistance R due to AC. AB and CD are perfect conductors. There is a magnetic field $B = B (+) \hat {k}$ If B is independent of time, obtain $V (t)$ assuming $V(0) = u_0$

asked Jan 1, 2017 by priyanka.c

1 answer

A magnetic field $B =B_o \sin(wt) \hat{k}$ covers a large region where a wire AB slides smoothly over two parallel conductors separated by a distance d, as shown in the fig. The wire are in the x-y plane. The wire AB (of length d) has resistance R and the parallel wires have negligible resistance. It AB is moving velocity $v$, what is the force needed to keep the wire at constant velocity ?

asked Jan 1, 2017 by priyanka.c

1 answer

A conducting wire XY of mass $m$ and negligible resistance slides smoothly on two parallel conducting wire as shown in the fig. The closed circuit has a resistance R due to AC. AB and CD are perfect conductors. There is a magnetic field $B = B (+) \hat {k}$ write down the equation for the acceleration of the wire XY.

asked Jan 1, 2017 by priyanka.c

1 answer

Consider a metal ring kept (supported by a cardboard) on top of a fixed solenoid carrying a current $I$ as shown in the fig : The centre of the ring coincides with the axis of the solenoid. If the current in the solenoid is switched off, What happens to the ring ?

asked Jan 1, 2017 by priyanka.c

1 answer

Consider a metal ring kept on top of a fixed solenoid (say on a cardboard) as shown in the figure. The centre of the ring coincides with the axis of the solenoid. If the current is suddenly switched on, the metal ring jumps up. Explain.

asked Dec 31, 2016 by priyanka.c

1 answer

A solenoid is connect to a battery so that a steady current flows through it. If an iron core is inserted into the solenoid, will the current increases or decreases ? Explain ?

asked Dec 31, 2016 by priyanka.c

1 answer

A wire in the form of a tightly wound solenoid is connected to DC source, and carries a current. If the coil is stretched so that spiral coil, will the current increases or decreases ? Explain.
(a) the current drawn from the d.c source increases
(b) the current drawn from d.c source decreases
(c) the current drawn first increases and then decreases
(d) the current drawn first decreases and then increases

asked Dec 31, 2016 by priyanka.c

1 answer

Consider a magnet surrounded by a wire with an on/off switch as shown in the fig. If the switch is thrown from the off position (open circuit) to the on position (closed circuit) will a current flow in the circuit ? Explain.
(a) Yes
(b) No
(c) Cannot be determine
(d) information not sufficient

asked Dec 31, 2016 by priyanka.c

1 answer

A circular coil expands radially in a region of magnetic field and no electromotive force is produced in the coil. The can be cause
(a) The magnetic field is constant
(b) The magnetic field is in the same plane as the circular coil and it may or may not vary
(c) The magnetic field has a perpendicular (to the plane of the coil) component whose magnitude is decreasing suitably.
(d) There is constant magnetic field in the perpendicular (to the plane of the coil) direction

asked Dec 31, 2016 by priyanka.c

1 answer

The mutual inductance $M_{12}$ of coil 1 with respect to coil 2.

asked Dec 31, 2016 by priyanka.c

1 answer

An emf is produced in a coil, which is not connected to an external voltage source. This can be due to <br/(a) the coil being in a time varying magnetic field
(b) the coil moving in a time varying magnetic field
(c) the coil moving in a constant magnetic field
(d) the coil is stationary in external spatially varying magnetic field, which does not change with time.

asked Dec 31, 2016 by priyanka.c

1 answer

An $emf$ is produced in a coil, which is not connected to an external voltage source. This can be due to
(a) The coil being in a time varying magnetic field
(b) The coil moving in a time varying magnetic field
(c) The coil moving in a constant magnetic field
(d) The coil is stationary is externally spatially varying magnetic field, which does not change with time.

asked Dec 31, 2016 by priyanka.c

1 answer

A metal plate is getting heated. It can be because of
(a) a direct current is passing through the plate.
(b) it is placed in a times varying magnetic field
(c) it is placed in a space varying magnetic field but does not varying with time
(d) a current (either direct or alternating ) is passing through the plate.

asked Dec 31, 2016 by priyanka.c

1 answer

The self inductance L of a solenoid of length $l$ and area of cross section A, with a fixed number of turns N increases as

asked Dec 31, 2016 by priyanka.c

1 answer

There are two coils A and B. A current starts flowing in B, the coil A is made to rotate about a vertical axis as shown in the fig. No current flows in B if A is at rest. The current in the coil A, when the current in B (at t = 0) is counter clockwise and the coil A is as shown at this instant t= 0 is
(a) constant current clockwise
(b) varying current clockwise
(c) varying current clockwise<br> (d) constant current counter clockwise.

asked Dec 31, 2016 by priyanka.c

1 answer

There are two coils A and B as shown in fig. A current starts flowing in B as shown, when A is moved towards B and stops when A stops moving. The current in A is counter-clockwise. B is kept stationary when A moves. We can infer that
(a) there is a constant current in the anticlockwise direction in A (b) there is a varying current in A
(c) there is no current in A
(d) there is a constant current in the counter clockwise direction in A

asked Dec 31, 2016 by priyanka.c

1 answer

A cylindrical bar magnet is rotated about its axis, as shown in fig. A wire is connected from the axis and is made to touch the cylindrical surface through a contact. Then
(a) a direct current flows in the ammeter A
(b) an alternating sinusoidal current flows through the ammeter A with a time period $T= \frac{2T}{w}$
(c) no current flows through the ammeter A
(d) a time varying non-sinusoidal current flows through the ammeter A

asked Dec 31, 2016 by priyanka.c

1 answer

A loop, made of straight edges has six corner at A(0, 0, 0), B(L, 0, 0), C(L, L, O), D(O, L,O), E(O, L, L) and F (0, 0, L). A magnetic field $B = B_o(\hat{i} + \hat{k})T$ is present in the region.
The flux passing through the loop ABCDEFA (in that order) is $(a)B_oL^2Wb$ $(b)2B_oL^2Wb$ $(c)\sqrt 2B_oL^2Wb$ $(d)4B_oL^2Wb$

asked Dec 31, 2016 by priyanka.c

1 answer

A square of side L metres lies in the x-y plane in a region, where the magnetic field is given by $B = B_o (2 \hat{i} +3 \hat{j} + 4 \hat{k}) T,$ where $B_o$ is constant. The magnitude of flux passing through the square $(a)\; 2B_oL^2 Wb$ $(b) \; 3B_o L^2 Wb$ $(c) \; 4B_o L^2 Wb$ $(d) \; \sqrt{29}B_o L^2 Wb$

asked Dec 31, 2016 by priyanka.c

1 answer

Evaluate the induced $emf$ in the loop if the wire carries a current of 50A and the loop has an instantaneous velocity $v = 10 m/s$ at the location $x= 0.2 m,$ as shown, Take $a = 0.1$ and assume that the loop has a large resistance.

asked Dec 31, 2016 by priyanka.c

1 answer

Obtain an expression for the mutual inductance between a long straight wire and a square of side a as shown in the figure .

asked Dec 31, 2016 by priyanka.c

1 answer

An air-cored solenoid with length 30cm, area of cross section $25 cm^2$ and number of turns 500, carries a current of 2.5A. The current is suddenly switched off in a brief time of $10^{-3}S.$ How much is the average back emf induced across the ends of the open switch in the circuit ? Ignore the variation in magnetic field near the ends of the solenoid ?

asked Dec 31, 2016 by priyanka.c

1 answer

How much power is dissipated as heat in the closed circuit ? What is the source of this power ?

asked Dec 31, 2016 by priyanka.c

1 answer

Figure shows a metal rod PQ resting on the smooth rail AB and positioned between the poles of a permanent magnet. The rail, the rod and the magnetic field are in three mutual perpendicular directions. A galvanometer G connects the rails through a switch K. Length of the rod = 15 cm, B = 0.50 T, resistance of the closed loop containing the rod = $9.0 m \Omega$. Assume the field to be uniform.
What is the induced emf in the moving rod if the magnetic field is parallel to the rails instead of being perpendicular?

asked Dec 31, 2016 by priyanka.c

1 answer

Figure shows a metal rod PQ resting on the smooth rail AB and positioned between the poles of a permanent magnet. The rail, the rod and the magnetic field are in three mutual perpendicular directions. A galvanometer G connects the rails through a switch K. Length of the rod = 15 cm, B = 0.50 T, resistance of the closed loop containing the rod = $9.0 m \Omega$. Assume the field to be uniform.

How much power is required at the same speed, to keep the rod moving at the same speed. (=12 cm/s) when k is closed ?

asked Dec 31, 2016 by priyanka.c

1 answer

Figure shows a metal rod PQ resting on the smooth rail AB and positioned between the poles of a permanent magnet. The rail, the rod and the magnetic field are in three mutual perpendicular directions. A galvanometer G connects the rails through a switch K. Length of the rod = 15 cm, B = 0.50 T, resistance of the closed loop containing the rod = $9.0 m \Omega$. Assume the field to be uniform.

what is the retarding force on the rod when k is closed ?

asked Dec 31, 2016 by priyanka.c

1 answer

Figure shows a metal rod PQ resting on the smooth rail AB and positioned between the poles of a permanent magnet. The rail, the rod and the magnetic field are in three mutual perpendicular directions. A galvanometer G connects the rails through a switch K. Length of the rod = 15 cm, B = 0.50 T, resistance of the closed loop containing the rod = $9.0 m \Omega$. Assume the field to be uniform.

With k open and the rod moving uniformly, there is no net force on the electrons in the rod PQ even though they do experience magnetic force due to the motion of the rod. Explain.

asked Dec 31, 2016 by priyanka.c

1 answer

Figure shows a metal rod PQ resting on the smooth rail AB and positioned between the poles of a permanent magnet. The rail, the rod and the magnetic field are in three mutual perpendicular directions. A galvanometer G connects the rails through a switch K. Length of the rod = 15 cm, B = 0.50 T, resistance of the closed loop containing the rod = $9.0 m \Omega$. Assume the field to be uniform.

Is there an excess charge built up at the ends of rods, when k is open ? What if k is closed ?

asked Dec 31, 2016 by priyanka.c

1 answer

Figure shows a metal rod PQ resting on the smooth rail AB and positioned between the poles of a permanent magnet. The rail, the rod and the magnetic field are in three mutual perpendicular directions. A galvanometer G connects the rails through a switch K. Length of the rod = 15 cm, B = 0.50 T, resistance of the closed loop containing the rod = $9.0 m \Omega$. Assume the field to be uniform.

Suppose K is open and the rod is moved with a speed of 12cm/s in the direction shown. Give the polarity and magnitude of the induced $emf$.

asked Dec 31, 2016 by priyanka.c

1 answer

It is desired to measure the magnitude of field between the poles of a powerful loud speaker magnet. A small flat search coil of area $2cm^2$ with closely wound turns, is positioned normal to the field direction and then quickly snatched out of the field region. Equivalently one can give it a quick $90^{\circ}$ turns to bring its plane parallel to the field direction. The total change flown in the coil (measured by a ballistic galvanometer connected to coil) is 7.5mc. The combined resistance of the coil and the galvanometer $0.50 \Omega$. Estimate the field strength of magnet.

asked Dec 30, 2016 by priyanka.c

1 answer

A square loop of side 12cm with its sides parallel to X and Y axes is moved with a velocity of 8 cm/s in the positive X-direction in an environment containing a magnetic field in the positive Z-direction. The field is neither uniform in space nor constant in time. It has a gradient of $10^{-3}$T/cm along the negative X-direction (that is it increases by $10^{-3}$T/cm as one moves in the negative X-direction) and it is decreasing in time at the rate of $10^{-3} $ T/S. Determine the direction and magnitude of the induced current in the loop if its resistance is $4.50 m\Omega$

asked Dec 30, 2016 by priyanka.c

1 answer

Suppose a rectangular loop of sides 8cm and 2cm with a small cut is stationary but the current feeding the electromagnet that produces the magnetic field is gradually reduced so that the field decreases from its initial value of 0.3T at the rate of 0.02T/S. If the cut is joined and the loop has a resistance of 1.6$ \Omega$, how much power is dissipated by the loop as heat? What is the source of this power ?

asked Dec 30, 2016 by priyanka.c

1 answer

A magnetic field in a certain region is given by $ B = B_0 cm (\omega t) \hat {k}$ and a coil of radius "a" with resistance R is placed in the x - y plane with its centre at the origin in the magnetic field, as shown in the fig. Find the magnitude and th direction of the current at (a, 0, 0) at $ t = \frac {\pi}{2\omega} \; and \; t = \frac {3 \pi}{2 \omega}$

asked Dec 30, 2016 by suganyadevi.p

1 answer

A rectangular loop of wire ABCD is kept close to an infinitely long wire carrying a current $ I (t) = I_0 (1 - \frac {t}{T}) for $ 0 \leq t \leq T$ and $ I (0) = 0$ for t > T, as shown in the fig. Find the total charge passing through a given point in the loop, in time T, The resistance of the loop is R.

asked Dec 30, 2016 by suganyadevi.p

1 answer

Consider an infinitely long wire carrying a current I(t), with $ \frac {dI}{dt} = \lambda = constant$. Find the current produced in the rectangular loop of wire ABCD if its resistance is R, as shown in the fig.

asked Dec 30, 2016 by suganyadevi.p

1 answer

A magnetic field B is confined to a region $r \leq a$ and points out the paper (the Z axis) $ r = 0$ being the centre of the circular region. A charged ring (charge = Q) of radius b $b>a$ and mass m lies in the xy plane with its centre at the origin. the ring is free to rotate and is at rest. The magnetic field is brought to zero in time $\bigtriangleup t$. Find the angular velocity $\omega$ of the ring after the field vanister.

asked Dec 30, 2016 by suganyadevi.p

1 answer

Give the expression for average value of a.c voltage $V = V_0\; sin \omega t$ over time interval $ t = 0 \; to \; t = \frac {\pi}{\omega}$

asked Dec 30, 2016 by suganyadevi.p

1 answer

A jet plane is travelling towards west at a speed of $1800\; km/hr$. What is the voltage difference developed between the ends of the wing having a span of 25m, if the earth's magnetic field at the location has a magnitude of $5 \times 10^{-4} T$ and the dip angle is $30^{\circ}$

asked Dec 30, 2016 by priyanka.c

1 answer

An electrical element x connected to an alternating voltage source has current through it leading the voltage by $\frac {\pi}{2}$ radius. Identify x and write an expression for its reactance.

asked Dec 30, 2016 by suganyadevi.p

1 answer

A pair of adjacent coils have a mutual inductance of 1.5 H. If the current in one is changed from $0 \; to\; 20 A$ is $0.5 S$ , what is the change of flux with the other coil.

asked Dec 30, 2016 by priyanka.c

1 answer

Self induction of an air core inductor increases from 0.01 MH to 10 MH on introducing an iron core into it. What is the relative permeability of the core used?

asked Dec 30, 2016 by suganyadevi.p

1 answer

The dimension of $\frac {h}{e}$ is the same as that of magnetic flux $\phi$. Say true or false.

asked Dec 30, 2016 by suganyadevi.p

1 answer

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