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Physics 4 Marks Questions

Electromagnetic Waves · Rajasthan Board (RBSE) STD 12 Science (Rajasthan - English Medium). 2 questions.

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4 Marks Questions

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2 questions · self-marked practice — reveal the answer and mark yourself.

Question 14 Marks
A metal rod is placed along the axis of a solenoid carrying a high-freqμency alternating current. It is found that the rod gets heated. Explain why the rod gets heated.
Answer
The magnetic field along the axis of a solenoid carrying a high-frequency alternating current changes continuously. Due to the change in the magnetic field, e.m.f (or eddy current) is induced in the metal rod. There will be flow of charge due to the induced e.m.f. The direction of the induced e.m.f changes very frequently due to the high-frequency alternating current in the solenoid. Thus, the rod gets heated up due to the flow of charge in it.
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Question 24 Marks
In a microwave oven, the food is kept in a plastic container and the microwave is directed towards the food. The food is cooked without melting or igniting the plastic container. Explain.
Answer
The natural frequency of water matches the frequency of microwave. This is the reason that food containing water gets cooked. The natural frequency of the plastic container does not match the frequency of microwave. So, the plastic container is not damaged.
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