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Electro magnatism

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Sudipta Bera
Vidyasagar University (VU), Midnapore
M.Sc Physics
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ELECTRO MAGNETISM ATTEMPT ALL THE QUESTIONS:- F.M-60 TIME-1.30hr 30x2=60 1. Why does a magnetic needle shows a deflection when brought close to a current carrying conductor? 2. A straight conductor passing vertically through a cardboard having some iron fillings sparkled on it. I. Show the arrangement of the iron fillings with direction when current flows upward. II. What happen if single conductor is replaced by several conductors? 3. Give a labelled diagram showing direction of current and three magnetic flux (inside) in a solenoid. 4. State two ways by which magnetic field in a solenoid can be increased. 5. When current is switched on in the diagram what happen. Give reason. 6. Name the material used in the armature of an electric bell. Give reason for your answer. 7. Draw a complete labelled diagram of an electric bell. 8. State the polarities developed at the end A and B. Which rule is applied here? 9. State two ways by which strength of an electromagnet can be increased. 10. State two advantage of electromagnet over permanent magnet. 11. State the function of split rings in a D.C motor. 12. How the direction of rotation of a D.C motor can be reversed? 13. State the effecting of inserting a soft iron core within the coil of a D.C motor. 14. A flat coil ABCD is freely suspended between the pole piece of a U shaped permanent magnet with the plain of coil parallel to magnetic field. I. What happen when current is passing in the coil? II. When will the coil come to rest? III. Name the instrument which makes use of the principle stated above. 15. A coil ABCD mounted on an axle is placed between the poles N and S of a permanent magnet as shown in fig. I. In which direction will the coil begin to rotate when current is Passed through the coil in direction ABCD. II. Why is a commutator necessary for continuous rotation of the coil? 16. What energy conversion does take place during the working of a D.C motor? 17. Two coils A and B are placed as shown in fig. The coil A is connected to a battery S and a key K, while the coil B is connected to a centre zero galvanometer G. What will you observe in the galvanometer when i. When the key is closed? ii. With the key closed, the coil B moved rapidly towards the coil B? iii. With the key closed, the coil A and B are moved with the same speed in same direction? 18. Difference between D.C motor and A.C generator. 19. 20. 21. 22. 23. 24. 25. 26. 27. 28. 29. 30. State Faraday s laws of electromagnetic induction. What is Lenz s law? Why is it more difficult to move a magnet towards a coil which has a large number of turns? Explain the significance of Lenz s law to show the conservation of energy in electromagnetic induction. a) Describe the observation if the coil is rapidly moved. b) How would the observation be altered if (a) the coil has twice as many turns,(b)the coil has made to move three times as first? Draw a labelled diagram of a simple a.c. generator. Suggest two ways in an a.c. generator to produce a higher e.m.f. Draw a labelled diagram of a device you would use to transform 200 V a.c. to 15 V a.c. name the device and explain how it works. Give its two uses. Name the material in the core of (a) electrical bell (b) electromagnet (c) D.C motor (d) A.C generator (e) transformer. The secondary windings of a transformer in which the voltage is stepped down are usually made of thicker wire than the primary. Explain why. The input and output voltage of a transformer are 220 V and 44 V respectively. Find (a) the turns ratio (b) the current in input circuit if the output current is 2 A. Name two kinds of energy losses that take place in the core of the transformer. How are they minimised?

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