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7. 10. 11. 12. 13. 14, 15. 16. 17. 18. 19. 20. A train is moving with uniform speed from north to south. Will any potential difference be induced between the ends of its axle ? Ans. Yes, because the axle cuts the magnetic flux of the earth’s vertical component By. The induced potential difference across the axle of a train is always the same whether it goes in north- south direction, or east-west direction or any other direction. Explain with reason. Ans. In each case, the magnetic flux of the earth’s vertical component By is cut. Awire pointing north-south is dropped freely towards earth. Will any potential difference be induced across its ends ? Ans. No, because no magnetic flux (By or By) will be cut. If the wire kept in east-west direction be dropped freely, then ? Ans. Yes, now it cuts the magnetic flux of the horizontal component B;, of earth’s field. A vertical metallic pole falls down through the plane of the magnetic meridian. Will any emf be induced between its ends ? Ans. No. It cuts neither By nor By. If a metallic plate be placed below an oscillating magnet, the magnet stops soon. Why ? Ans. Eddy currents are produced in the plate which oppose the motion of the magnet. Write the dimensional formula for the mutual inductance of two coils. Ans. (ML? T A}, same as that of L. If two coils are very tightly wound, one over the other, will M increase or decrease as compared to the case when the coils are placed some distance apart ? Ans. M will increase. Define self inductance of a coil. Write its SI unit. (AI CBSE 2010, CBSE 2009, Delhi) Name two factors on which the self-inductance of an air-core coil depends. Ans. Number of turns in the coil and its radius. How does the self-inductance of a coil depend on the number of turns of the coil ? Ans. L « N?. Give two factors on which self-inductance of a long solenoid depends. Ans. Number of turns, permeability of core material. If the number of turns of a solenoid is doubled, keeping the other factors constant, how does the self- inductance of the solenoid change ? Ans. L becomes 4 times the initial value. What is the effect of metallic core on the self- inductance of a coil or of a solenoid ? Ans. It increases. Scanned by CamScanner 21. Name the quantity in electrical circuits which plays the same role as inertia in mechanics. Ans. Inductance. 22. How does the mutual inductance of a pair of coils change when (i) distance between the coils is increased and (ii) number of turns in the coils is increased ? (AI CBSE 2013 ) Ans. (i) decreased (ii) increased. 23. The motion of copper plate is damped when it is allowed to oscillate between the two poles of a magnet. What is the cause of this damping ? (AI CBSE 2013) 34. When primary coil S P P is moved towards secondary coil S as ol <_ shown in __ figure, | | the galvanometer G = H + shows momentary deflection. (i) What can be done to have larger deflections in the galvanometer with the same battery. (ii) State the related law. (CBSE 2010, Dethi) Ans. (i) Coil P should be moved at a faster rate. (ii) Faraday’s first law, e « we ; 35. A coil Q is connected to low voltage bulb B and placed near another coil P as shown in figure. Give reason to explain the following : B a.c. | SOURCE Le {—~/,. NS SSO OO —~9200 0, Q P (i) The bulb lights. (ii) Bulb gets dimmer if coil Q is moved away from P. (CBSE 2010, Dethi) Ans. (i) Due to variation in the magnitude of current of AC source the flux associated with coil P and hence with coil Q is changing continuously, as a result a current is induced in coil Q due to which bulb B lights. (ii) When coil Q is moved away from P, the rate of change of magnetic flux linked with coil Q decreases, so lesser current is induced in coil Q. 36. Two identical loops one of copper and the other of aluminium, are rotated with the same angular speed in the same magnetic field. Compare (i) the induced emf and (ii) the current produced in the two coils. Justify your answer. (AI CBSE 2010) Ans. (i) emf is equal in both (ii) current is larger in copper loop due to its lesser resistance. Scanned by CamScanner 
