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1. The direction of induced emf is always such that it opposes the factor that produces the induced emf. Therefore, induced emf is also called back emf.


2. No, current will be induced only if the circuit is complete but emf wil always be induced whenever there is change in magnetic flux associated with a loop.


3. This is not possible. Current can be induced only by changing the magnetic flux through the loop. It does not matter whether the field is strong or weak.


4. No current is induced in either case. Current can not be induced by changing the electric flux.


5. 1. Anti-clockwise
   2. No current
   3. Clockwise


6. The induced emf will be constant in the case of the rectangular loop. In the case of circular loop, the rate of change of area of the loop during its passage out of the field is not constant. Hence induced emf will also vary.


7. When the bar magnet moves towards the ring, the magnetic flux linked with the ring changes. Consequently, a current is induced in the ring. According to Lenz's law, the direction of induced current is such that it opposes the cause (i. e. the motion of the magnet towards the ring) which produces it. Thus, the acceleration of the falling magnet becomes less the acceleration due to gravity.


8. Yes, he can detect the presence of magnetic field by connecting the galvanometer to the coil and then rotating the coil. If there is deflection in the galvanometer, then the magnetic field is present on the planet, otherwise not.


9. Equal and opposite currents flow in a wire doubled up on itself. These currents cancel out the magnetic fields produced by each other and hence, no emf is induced emf in such coils. In other words, the inductive effect of the coils is minimized.


10. No. There will be no emf induced in the rod if it falls vertically because it does not cut any component of earth's field.


11. More work will be done in (a). The induced emf and hence the repulsive force opposing the motion of the loop will be more if it is moved rapidly.


12. It is non conservative field as work done to move the charge around a closed path in this field is not zero.


13. Whether the copper plate is pushed into a magnetic field or pulled out of it, the magnetic flux linked with plate changes and hence, there will be a force acting on the plate opposing the motion of the plate due to the induced current.


14. The magnetic flux linked with the coils increases if they are brought closer. Hence, according to Lenz's law, an ernf is induced in each coil which opposes the change of flux. Therefore, the currents in each coil will decrease.


15. No emf will be induced because it is the change in magnetic field that produced the induced emf, not the change in electric field.


16. No emf will be induced in the coil as the net change of magnetic flux in the coil is zero. This happens because the magnets move in the same direction with the same speed.


17. The magnetic field due to current flowing in the wire XY passing through the ring is perpendicular to the plane of the ring and is directed outwards. As the current in the wire XY increases, magnetic field also increases. But according to Lenz's law, the current induced in the ring must flow so as to oppose the increasing magnetic of the current in the wire. So, induced current should produce a magnetic field in a direction opposite to that of the current in the wire, i.e., inwards. Obviously, the induced current in the loop flows in the clockwise direction.


18. The magnetic flux linked with the ring due to a steady current in XY does not change. Therefore, no current will be induced in the loop.


19. When the magnet is moved as shown, end B of the coil AB becomes north pole because N-pole of the magnet moves towards it (Lenz's law) and end C of the coil CD also becomes north pole because Spole of the magnet moves away from it Lenz's law). Hence, the induced currents in the coils flow anticlockwise when viewed from the magnet.


20. There will be no emf induced in the conductor as the Lorentz force acting on the charges (free electrons) in the conductor will be zero and hence, no displacement of charges towards the ends will take place.
    

CBSE Electromagnetic Induction ( With Hint / Solution)
Class XII (By Mr. Ashis Kumar Satapathy)
email - [email protected]

Electromagnetic Induction