CBSE Questions for Class 12 Medical Physics Electromagnetic Induction Quiz 3 - MCQExams.com

A solenoid (air core) ahs 400 turns, is 20 cm long and has a cross section of $$4 cm^2$$. Then the coefficient of self induction is approximately
  • $$4\times 10^{-5} H$$
  • $$4\times 10^{1} H$$
  • $$4\times 10^{-4} H$$
  • $$4 H$$
Two coils of self inductances 2 mH and 8 mH are placed so close together that the effective flux in one coil is completely linked with the other. The mutual inductance between these coils is:
  • 10 mH
  • 6 mH
  • 4 mH
  • 16 mH
A solenoid is connected to a source of constant e.m.f. for a long time. A soft iron piece is inserted into it. Then, which of the following is/are correct?
  • Self-inductance of the solenoid gets increased
  • Flux linked with the solenoid increases; hence, steady state current gets decreased
  • Energy stored in the solenoid gets increased
  • Magnetic moment of the solenoid gets increased
The current I in an induction coil varies with time t according to the graph shown in the figure. Which of the following graphs shows the induced emf $$(\varepsilon)$$in the coil with time

73951_4c70aa3aa3dd4f8e9b2b8c14cae06daf.png
Magnetic flux $$\phi$$ (in weber) linked with a closed circuit of resistance $$10 \Omega$$ varies with time t (in second) as $$\phi   = 5{t^2} - 4t + 1$$. The induced electromotive force in the circuit at t = 0.2 second is
  • 0.4 V
  • -0.4 V
  • -2.0 V
  • 2.0 V
A circular disc of radius 0.2 metre is placed in a uniform magnetic field of induction $$\dfrac{1}{\pi }\left ( \dfrac{wb}{m^{2}} \right )$$ in such a way that its axis makes an angle of 60 with $$\vec{B}$$ The magnetic flux linked with the disc is:
  • 0.058 wb
  • 0.01 wb
  • 0.02 wb
  • 0.06 wb
  • Both Assertion and Reason are correct and Reason is the correct explanation for Assertion
  • Both Assertion and Reason are correct but Reason is not the correct explanation for Assertion
  • Assertion is correct but Reason is incorrect
  • Both Assertion and Reason are incorrect
The frequency of A.C mains in India is
  • $$30 Hz$$
  • $$50Hz$$
  • $$60Hz$$
  • $$120Hz$$
Read the following statements and answer whether the given statement is true or false.

The magnitude of induced current can be increased by increasing the number of turns in coil.
  • True
  • False
A conducting disc of radius r spins about its axis with an angular velocity $$\omega$$. There is a uniform magnetic field of magnetude B perpendicular to the plane of the disc. C is the centre of the ring.
  • No emf is induced in the disc.
  • The potential difference between C and the rim is $$\frac{1}{3} Br^2 \omega$$.
  • C is at a higher potential than the rim.
  • Current flows between C and the rim.
Read the following statements and answer whether the given statement is true or false.
In a generator, magnitude of the induced current can be increased by decreasing the speed of rotation of armature.
  • True
  • False
Whenever current is changed in a coil, an induced e.m.f. is produced in the same coil, This property of the coil is due to
  • mutual induction
  • self induction
  • eddy currents
  • hysteresis
Read the following statements and answer whether the given statement is true or false.
The induced e.m.f. depends only on the no of turns of the coil:
  • True
  • False
Whenever the magnetic flux linked with a coil changes, an
induced e.m.f. is produced in the circuit. The e.m.f. lasts
  • for a short time
  • for a long time
  • for ever
  • so long as the change in flux takes place
A conducting loop is placed in a uniform magnetic field with its plane perpendicular to the field. An emf is induced in the loop if
  • it is translated
  • it is rotated about its axis
  • it is kept untouched for several minutes
  • it is cut into two pieces
To obtain maximum EMF from a number of cells, they must be connected in
  • Series
  • Parallel
  • Both (a) and (b) above
  • None of these
A solenoid of inductance $$L$$ and length $$l$$ and mass $$m$$, whose windings are made of material of density $$D$$ and resistivity is $$\rho$$,(the winding resistance is $$R$$). Find out the inductance in terms of others.
  • $$\dfrac {\mu_0}{4\pi l}\dfrac {Rm}{\rho D}$$
  • $$\dfrac {\mu_0}{4\pi R}\dfrac {lm}{\rho D}$$
  • $$\dfrac {\mu_0}{4\pi l}\dfrac {R^2m}{\rho D}$$
  • $$\dfrac {\mu_0}{2\pi R}\dfrac {lm}{\rho D}$$
The self induction takes place when magnetic flux through a coil :
  • Remains steady
  • Decreases
  • Increases
  • Either (B) or (C)
In alternating current
  • The direction of current is always positive
  • The direction of current is always negative
  • The direction of current changes constantly
  • The direction of current is either positive or negative
A toroid is wound over a circular core with total no. of turns equal to $$N$$. The radius of each turn is $$r$$ and radius of toroid is $$R (> > r)$$. The coefficient of self-inductance of the toroid is given by
120763.png
  • $$L=\dfrac {\mu_0Nr^2}{2R}$$
  • $$L=\dfrac {\mu_0Nr}{2R}$$
  • $$L=\dfrac {\mu_0Nr^2}{R}$$
  • $$L=\dfrac {\mu_0N^2r^2}{2R}$$
The emf produced in a wire by its motion across a magnetic field does not depend upon
  • length of the wire
  • composition of the wire
  • speed of the wire
  • orientation of the wire
Magnitude of e.m.f. produced in a coil when a magnet is inserted into it does not depend upon :
  • Number of turns in the coil
  • Speed of the magnet 
  • Magnetic strength of magnet
  • Temperature of coil 
A magnet is moved towards a coil, first quickly and then slowly. The induced e.m.f. produced is :
  • Larger in first case
  • Smaller in first case
  • Equal in both cases
  • Larger or smaller, depending upon resistance of the coil
Magnetic flux during time interval $$\tau$$ varies through a stationary loop of resistance $$R$$, as $$\phi_B = at (\tau - t)$$. Find the amount of heat generated during that time. Neglect the inductance of the loop.
  • $$\displaystyle \dfrac{a^2 \tau^3}{R}$$
  • $$\displaystyle \dfrac{a^2 \tau^2}{2R}$$
  • $$\displaystyle \dfrac{a^2 \tau^3}{3R}$$
  • $$\displaystyle \dfrac{a^2 \tau^3}{4R}$$
The two rails of railway track, insulated from each other and from the ground, are connected to a mill voltmeter. What will be the reading of the milli voltmeter when a train travels on the track at a speed of $$180 km/hr$$ and earth's magnetic field is $$0.2 \times 10^{-4}T$$ and the rails are separated by 1m.
  • 1 m v
  • 2 m v
  • 3 m v
  • 4 m v
The length of a wire required to manufacture a solenoid of length $$l$$ and self-induction $$L$$ is (cross-sectional area is negligible)
  • $$\sqrt {\dfrac {2\pi Ll}{\mu_0}}$$
  • $$\sqrt {\dfrac {\mu_0Ll}{4\pi}}$$
  • $$\sqrt {\dfrac {4\pi Ll}{\mu_0}}$$
  • $$\sqrt {\dfrac {\mu_0Ll}{2\pi}}$$
In the process of electromagnetic induction, the magnitude of the induced emf does not depend on _______. 
  • The number of turns of the coil
  • The magnetic flux linked with the coil
  • The rate of change of magnetic flux linked with the coil
  • Area of the coil
A wire of fixed length is wound on a solenoid of length $$l$$ and radius $$r$$. Its self-inductance is found to be $$L$$. Now, if the same wire is wound on a solenoid of length $$l/2$$ and radius $$r/2$$, then the self-inductance will be
  • $$2L$$
  • $$L$$
  • $$4L$$
  • $$8L$$
A magnet is made to oscillate with a particular frequency passing through a coil as shown in figure. The time variation of the magnitude of emf generated across the coil during one cycle is
145639_644d52706bf34f0c9be90ef4afe36a3b.png
Two coils X and Y are linked such that emf $$E$$ is induced in Y when the current in X is changing at the rate $$I'(=dI/dt)$$. If a current $$I_0$$ is now made to flow through Y, the flux linked with X will be
  • $$EI_0I'$$
  • $$\dfrac {I_0I'}{E}$$
  • $$\left (\dfrac {E}{I_0}\right )I'$$
  • $$\left (\dfrac {E}{I'}\right )I_0$$
The induction coil works on the principle of
  • self induction
  • mutual induction
  • amperes rule
  • fleming's right hand rule
The network shown in the figure is part of a complete circuit. If at a certain instant, the current $$I$$ is $$5A$$ and it is decreasing at a rate of $$10^{3} As^{-1}$$ then $$V_{B}-V_{A}$$ equals :
123978_8953f230732a48169d4658f1be8b4a95.png
  • $$20 V$$
  • $$15 V$$
  • $$10 V$$
  • $$5 V$$
The time constant of an inductance coil is $$2\times 10^{-3}s$$. When a $$90\Omega$$ resistance is joined in series, the same constant becomes $$0.5\times 10^{-3}s$$. The inductance and resistance of the coil are
  • $$30 mH; 30\Omega$$
  • $$60 mH; 30\Omega$$
  • $$30 mH; 60\Omega$$
  • $$60 mH; 60\Omega$$
Two coils are at fixed locations. When coil 1 has no current and the current in coil 2 increases at the rate of $$15.0 As^{-1}$$, the emf in coil 1 is $$25 mV$$. When coil 2 has no current and coil 1 has a current of $$3.6A$$, the flux linkage in coil 2 is
  • $$16 mWb$$
  • $$10 mWb$$
  • $$4.00 mWb$$
  • $$6.00 mWb$$
Calculate the inductance of a unit length of a double tape line as shown in figure. The tapes are separated by a distance $$h$$ which is considerably less than their width $$b$$.
120780.png
  • $$\dfrac {\mu_0h}{b}$$
  • $$\dfrac {\mu_0h}{2b}$$
  • $$\dfrac {2\mu_0h}{b}$$
  • $$\dfrac {\sqrt 2\mu_0h}{b}$$
The self inductance of the toroidal solenoid described in the passage is

143034.png
  • $$\dfrac {\mu_0N^2h}{2\pi}$$
  • $$\dfrac {\mu_0N^2h}{2\pi}log_e\dfrac {b}{a}$$
  • $$\dfrac {\mu_0Nh}{2\pi}log_e\dfrac {b}{a}$$
  • $$\dfrac {\mu_0N^2h}{2\pi}log_e\dfrac {a}{b}$$
The coil is wound on an iron core and looped back on itself so that core has two sets of closely wound coils carrying current in opposite directions. The self inductance is
  • $$0$$
  • $$2L$$
  • $$2L + M$$
  • $$L + 2M$$
When a current of 5 A flows in the primary coil then the flux linked with the secondary coil is 200 weber. The value of coefficient of mutual induction will be
  • 1000 H
  • 40 H
  • 195 H
  • 205 H
The electric flux through a certain area of dielectric is $$8.76 \times 10^3 t^4$$. The displacement current through the area is $$12.9 pA$$ at $$t = 26.1 ms$$ . Find the dielectric constant of the material.
  • $$2 \times 10^{-8}$$
  • $$4 \times 10^{-8}$$
  • $$8 \times 10^{-8}$$
  • $$2 \times 10^{-7}$$
Find the approximate value of induced current assuming the resistance to the current is confined to the square.
145930.png
  • $$\displaystyle \dfrac{BL \omega dt}{\rho}$$
  • $$\displaystyle \dfrac{BL^2 \omega dt}{\rho}$$
  • $$\displaystyle \dfrac{BL^2 \omega d}{\rho}$$
  • $$\displaystyle \dfrac{BL \omega d^2}{\rho}$$
A tank containing a liquid has turns of wire wrapped around it, causing it to act as an inductor. The liquid content of the tank can be measured by using its inductance to determine the height of the liquid level in the tank. The inductance of the tank changes from a value of $$L_0$$ corresponding to a relative permeability of $$1$$ when the tank is empty to value $$L_f$$ corresponding to a relative permeability $$X_m$$ (relative permeability of liquid) when the tank is full. The appropriate electronic circuit can determine the inductance correct upto $$5$$ significant figures and thus the effective relative permeability of the combined air and liquid within the rectangular has height $$D$$. The height of the liquid level in the tank is $$d$$. Ignore the fringing effects. Assume tank is fitted with $$Hg    X    _{Hg} = 2.9 \times 10^5$$.
Express $$d$$ as a function of $$L$$, inductance corresponding to a certain liquid height $$L_0, L_f$$ and $$D$$.
  • $$\displaystyle d =\frac{(L - L_0)D}{L_f - L_0}$$
  • $$\displaystyle d =\frac{LD}{L_f - L_0}$$
  • $$\displaystyle d =\frac{(L - L_0)D}{L_f }$$
  • None of these
A conducting loop is placed in a uniform magnetic field with its plane perpendicular to the field. An emf is induced in the loop if :
  • it is translated
  • it is rotated about its axis
  • it is rotated about a diameter
  • it is deformed
The self inductance of a motor of an electric fan is $$10 H$$. In order to impart maximum power at $$50 Hz$$, it should be connected to a capacitance of :
  • $$\displaystyle 4\mu F$$
  • $$\displaystyle 8\mu F$$
  • $$\displaystyle 1\mu F$$
  • $$\displaystyle 2\mu F$$
How many meters of a thin wire are required to design a solenoid of length $$1 m $$ and $$L = 1mH$$? Assume cross-sectional diameter is very small.
  • $$10 m$$
  • $$40 m$$
  • $$70 m$$
  • $$100 m$$
  • $$140 m$$
A small, conducting circular loop is placed inside a long solenoid carrying a current. The plane of the loop contains the axis of the solenoid. If the current in the solenoid is varied. The current induced in the loop is
  • clockwise
  • anti-clockwise
  • zero
  • clockwise or anti-clockwise depending on whether the resistance is increased or decreased
Two coils P and Q are lying parallels and very close to each other. Coil P is connected to an AC source whereas Q is connected to a sensitive galvanometer. On pressing key K
  • small variations are observed in the galvanometer for applied 50 Hz voltage
  • deflections in the galvanometer can be observed for applied voltage of 1 Hz to 2 Hz.
  • no deflection in the galvanometer will be observed
  • constant deflection will be observed in the galvanometer for 50 Hz supply voltage
When the number of turns per unit length in a solenoid is doubled then its coefficient of self induction will become
  • half
  • double
  • four times
  • unchanged
The number of turns in an air core solenoid of length 25 cm and radius 4 cm isIts self inductance will be
  • $$5 \times 10^{-4} H$$
  • $$2.5 \times 10^{-4} H$$
  • $$5.4 \times 10^{-3} H$$
  • $$2.5 \times 10^{-3} H$$
A cycle wheel with 64 spokes is rotating with N rotations per second at right angles to horizontal component of magnetic field. The induced emf generated between its axle and rim is E. If the number of spokes is reduced to 32 then the value of induced emf will be :
  • E
  • 2E
  • $$\displaystyle \frac{E}{2}$$
  • $$\displaystyle \frac{E}{4}$$
The maximum value of induced emf in a coil rotating in magnetic field does not depend on
  • the resistance of coil
  • the number of turns in the coil
  • the area of the coil
  • rotational frequency of the coil
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