Video Lecture
Theory For Making Notes
Practice Questions (Basic Level)
Q.1
In the given figure a conducting rod is held between the poles of a permanent magnet. An electric potential difference will be induced between the ends of the conductor when it is moved in the direction of
(a) P (b) Q (c) L (d) M
Ans. (d)
Q.2
A wire frame ABCD and a current – carrying conductor xy lie in the same plane. Now of the frame is rotated about xy.
(a) No current will flow in ABCD
(b) Current will flow in the direction ABCDA
(c) Current will flow in the direction ADCBA
(d) The current will depend on distance x between xy and AB.
Ans. (a)
Q.3
Two identical co-axial circular loops carry a current i, each circulating in the same direction. If the loops approach each other then
(a) Current in each increases
(b) The current in each decreases
(c) The current in each remains same
(d) The current in 1 increases where as current in 2 decreases
Ans. (b)
Q.4
A conducting circular loop is placed inside a long solenoid carrying a current, such that the plane of loop is parallel to the axis of solenoid. If the current in the solenoid is varied, the induced current in the loop will be
(a) clockwise
(b) anticlockwise
(c) zero
(d) depends on the direction of current in solenoid
Ans. (c)
Q.5
In the figure, the key K is pressed to close the circuit of the solenoid X. Which of the following statements A to E is correct?
(a) a momentary currents flows in the solenoid Y circuit, from R to Q
(b) no current flows along QR
(c) the coil Y is attracted to X
(d) a momentary current flows from Q to R
Ans. (d)
Q.6
A solenoid in horizontal position, connected to a battery and a switch is placed on a table. A copper ring is placed at some distance apart with its axis coinciding with solenoid. and is at a distance. When current is allowed through by closing the switch. The ring will
(a) remain stationary
(b) move towards the solenoid
(c) move away from the solenoid
(d) will rotate about the axic
Ans. (a)
Q.7
The magnetic flux F(in weber) in a closed circuit of resistance 10 ohm varies with time t (in seconds) according to equation F = 6t2 – 5t + 1. The magnitude of induced current at
t = 0.25 s is
(a) 1.2 A (b) 0.8 A (c) 0.6 A (d) 0.2 A
Ans : (d)
Q.8
According to Faraday’s law of electromagnetic induction,
(a) an electric field is produced by time-varying magnetic flux
(b) a magnetic field is produced by time-varying electric flux
(c) a magnetic field is associated with a moving charge
(d) none of the above
Ans : (a)
Q.9
Lenz’s law is a consequence of the law of conservation of
(a) charge (b) mass (c) momentum (d) energy
Ans : (d)
Q.10
Faraday’s law of electromagnetic induction is related to the
(a) law of conservation of charge
(b) law of conservation of energy
(c) third law of motion
(d) law of conservation of angular momentum
Ans : (b)
Q.11
A coil area A = 0.5 m2 is situated in a uniform magnetic field B = 4 Wb/m2 and makes an angle of 60° with respect to the magnetic field as shown. The value of the magnetic flux through the area A would be equal to :
(a) 2 weber
(b) 1 weber
(c) 3 weber
(d) (3/2) weber
Ans. (b)
Q.12
A magnet is moving towards a coil along its axis and the emf induced in the coil is e. If the coil also starts moving towards the magnet with the same speed, the induced emf will be
(a) e/2 (b) e (c) 2e (d) 4e
Ans : (c)
Q.13
An electron moves on a straight line path XY as shown in figure. The abcd is a coil adjacent to the path of electron. What will be the direction of current if any induced in the coil?
(a) No current is induced
(b) abcd
(c) adcb
(d) The current will reverse direction as the electron goes past the coil.
Ans. (b)
Q.14
In the figure, the flux through the loop perpendicular to the plane of the coil and directed into the paper is varying according to the relation,
F = 6t2 + 7t + 1
where F is in milliweber and t is in seconds. The magnitude of the emf induced in the loop at t = 2 s and the direction of induced current through R are
(a) 39 mV; right to left
(b) 39 mV; left to right
(c) 31 mV; right to left
(d) 31 mV; left to right
Ans. (d)
Q.15
A rectangular coil is placed in a region having a uniform magnetic field B perpendicular to the plane of the coil. An emf will not be induced in the coil if the
(a) magnetic field is increased uniformly
(b) magnetic field is switched off
(c) coil is rotated about the axis XOX¢
(d) coil is rotated about an axis perpendicular to the plane of the coil and passing through its centre O.
Ans. (d)
Q.16
A copper ring having a cut such as not to form a complete loop is held horizontally and bar magnet is dropped through the ring with its length along the axis of the ring. The acceleration of the falling magnet is
(a) g
(b) less than g
(c) more than g
(d) depends on the relative size of the cut
Ans : (a)
Practice Questions (Main Level)
Q.1
A varying magnetic flux linking a coil is given by: f = xt2. If at a time t = 3 sec, the e.m.f. induced is 9V, then the value of x is
(a) 0.66 Wbs–2
(b) 1.5 Wbs–2
(c) –0.66 Wbs–2
(d) –1.5 Wbs–2
Ans. (d)
Q.2
If the flux of magnetic induction through a coil of resistance R and having n turns changes from f1 to f2, then the magnitude of the charge that passes through the coil is
(a) \frac{{\left( {{{\varphi }_{2}}-{{\varphi }_{1}}} \right)}}{R}
(b) \frac{{n\left( {{{\varphi }_{2}}-{{\varphi }_{1}}} \right)}}{R}
(c) \frac{{\left( {{{\varphi }_{2}}-{{\varphi }_{1}}} \right)}}{{nR}}
(d) \frac{{nR}}{{\left( {{{\varphi }_{2}}-{{\varphi }_{1}}} \right)}}
Ans. (b)
Q.3
A coil having an area A0 is placed in a magnetic field which changes from B0 to 4B0 in time interval t. The average e.m.f. induced in the coil will be
(a) \frac{{3{{A}_{0}}{{B}_{0}}}}{t}
(b) \frac{{4{{A}_{0}}{{B}_{0}}}}{t}
(c) \frac{{3{{B}_{0}}}}{{{{A}_{0}}t}}
(d) \frac{{4{{B}_{0}}}}{{{{A}_{0}}t}}
Ans. (a)
Q.4
If a coil of metal wire is kept stationary in a non uniform magnetic field,
(a) an emf and current are both induced in the coil
(b) a current but no emf is induced in the coil
(c) an emf but no current is induced in the coil
(d) neither emf nor current is induced in the coil
Ans. (d)
Q.5
If f-magnetic flux, y-electric flux and t-time. The dimension of {{\left( {\frac{{d\psi }}{{dt}}} \right)}}/{{\left( {\frac{{d\varphi }}{{dt}}} \right)}}\; is equal to
(a) Charge (b) Force (c) Velocity (d) Capacitance
Ans. (c)
Q.6
A conducting rod PQ is moving parallel to x-z-plane in a uniform magnetic field directed in the positive y-direction. The end P of the rod will become
(a) sometime positive and sometime negative
(b) positive
(c) neutral
(d) negative
Ans. (d)
Q.7
What is direction of induced current in the coil as shown in the figure? (If rate of increase of current is equal to the rate of decrease)
(a) clockwise
(b) anticlockwise
(c) zero
(d) not defined with same rate
Ans. (c)
Q.8
A metallic wire bent into a right Dabc moves with a uniform velocity v as shown in the figure, B is the strength of uniform magnetic field perpendicular outwards the plane of triangle. The net emf is and emf along ab is
(a) zero, Bv(bc) with b positive
(b) zero, Bv(bc) with a positive
(c) Bv(bc) with c positive, zero
(d) Bv(bc) with b positive, zero
Ans. (b)
Q.9
A very long uniformly charged rod falls with a constant velocity V through the center of a circular loop. Then the magnitude of induced emf in loop is
(charge per unit length of rod = l)
(a) \frac{{{{\mu }_{0}}}}{{2\pi }}\lambda {{V}^{2}}
(b) \frac{{{{\mu }_{0}}}}{2}\lambda {{V}^{2}}
(c) \frac{{{{\mu }_{0}}}}{{2\lambda }}V
(d) zero
Ans. (d)
Q.10
When magnetic flux passing through a loop is changed, an induced current is produced in the circuit. If charge flows in the circuit is Dq and Dt is the time interval for which flux is changing, then the graph between Dq and Dt is
Ans. (b)
Practice Questions (JEE Advance Level)
Q.1
A plane loop as shown in figure is shaped as two squares with sides a = 20 cm and b = 10 cm and is introduced into a uniform magnetic field at right angles to the loop’a plane. The magnetic induction varies with time as B = Bo sin wt, where Bo = 10 mT and w = 100 s-1. If its resistance per unit length is equal to r = 50 mW m-1,the amplitude of the current induced in the loop should be
(a) 0.5A (b) 0.2A
(c) 0.8A (d) 1.2A
Ans . (a)
Q.2
A square wire frame with side a and a straight conductor carrying a constant current I are located in the same plane. The inductance and the resistance of the frame are equal to L and R respectively. If the frame is turned through 180° about the axis OO¢ separated from the current carrying conductor by a distance b, then the electric charge flown through the frame is
(a) \frac{{3{{\mu }_{o}}aI}}{{2\pi R}}\,\ln \,\left| {\frac{{b+a}}{{b-a}}} \right|
(b) \frac{{{{\mu }_{o}}(a+b)I}}{{2\pi R}}\,\ln \,\left| {\frac{{b+a}}{{b-a}}} \right|
(c) \frac{{{{\mu }_{o}}aI}}{R}\,\ln \,\left| {\frac{{b+a}}{{b-a}}} \right|
(d) \frac{{{{\mu }_{o}}aI}}{{2\pi R}}\,\ln \,\left| {\frac{{b+a}}{{b-a}}} \right|
Ans : (d)
Q.3
The magnetic field at a certain region is given by \overrightarrow{{B\,}}=\frac{1}{\pi }(\hat{i}-2\hat{j}) Tesla. Find the flux associated with a region represented by {{y}^{2}}+{{z}^{2}}-8=0
(a) 8 unit
(b) 16 unit
(c) 24 unit
(d) Zero
Ans. (a)
Q.4
The magnetic flux associated with metal ring varies with time according to
\varphi =3(a{{t}^{3}}-b{{t}^{2}})\text{T}{{\text{m}}^{2}}. with \displaystyle a=2{{\sec }^{{-3}}},b=6{{\sec }^{{-2}}}. If the resistance of the ring is 3W, the maximum current induced in the ring during the time interval from t = 0 to t = 2 sec is
(a) 2 amp
(b) 4 amp
(c) 6 amp
(d) Zero
Ans. (d)
Q.5
Loop A of radius {{\left( {\frac{{d\psi }}{{dt}}} \right)}}/{{\left( {\frac{{d\varphi }}{{dt}}} \right)}}\; moves towards a constant current carrying loop B with a constant velocity v in such a way that their planes are parallel and coaxial. The distance between the loops when the induced emf in loop A is maximum is
(a) R
(b) \frac{R}{{\sqrt{2}}}
(c) \frac{R}{2}
(d) R\left( {1-\frac{1}{{\sqrt{2}}}} \right)
Ans. (c)