Catholic High 2004 Prelims P2 Q9b
The figure below shows a coil of wire wound on a piece of soft iron. A magnet is rotated in the gap in the soft iron as shown. When the magnet rotates, the lamp connected to the coil glows. The magnet takes 0.20s to make one complete revolution.
(i) Explain why the lamp glows when the magnet rotates.
(ii) Describe 2 alterations that can be made to the parts of the apparatus for the lamp to glow more brightly.
(iii) If the U-shaped soft iron is removed, would the lamp stil lglow when the magnet rotates? Explain your answer.
(iv) The lamp is marked 6.0 V, 36 W. Explain this statement.
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Answer:
(i) There is an induced emf generated at the ends of the coil, producing a current in the lamp due to changing magnetic flux linkage produced when the coil rotates.
(ii) Any 2
1) Increase the number of turns of the coil.
2) Rotate the magnet faster
3) Use a stronger magnet
(iii) Yes, there will still be a changing magnetic flux linkage, but the glow is weaker due to poorer flux linkage.
(iv) The lamp requires a normal working voltage of 6.0 V for it to convert energy into light at a rate of 36 J per second.
