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A magnetic needle suspended horizontally...

A magnetic needle suspended horizontally by an unspun silk fibre, oscillates in the horizontal plane because of the restoring force originating mainly from

A

The torsion of the silk fibre

B

The horizontal component of earth's magnetic field

C

The force of gravity

D

All the above factors

Text Solution

AI Generated Solution

The correct Answer is:
To solve the question, we need to identify the restoring force that causes a magnetic needle suspended horizontally by an unspun silk fiber to oscillate in the horizontal plane. ### Step-by-Step Solution: 1. **Understanding the Setup**: A magnetic needle is suspended and can rotate freely in the horizontal plane. It is influenced by the Earth's magnetic field. 2. **Identifying Forces**: The magnetic needle experiences a torque due to the Earth's magnetic field. When the needle is displaced from its equilibrium position, a restoring torque acts on it. 3. **Restoring Force Origin**: The restoring force that brings the needle back to its equilibrium position primarily originates from the horizontal component of the Earth's magnetic field. This is because the magnetic needle aligns itself with the magnetic field lines. 4. **Evaluating Options**: - **Option A**: Origin of the silk fiber - This is not correct as the silk fiber merely suspends the needle. - **Option B**: Horizontal component of Earth's magnetic field - This is correct as it provides the necessary torque to restore the needle to its equilibrium position. - **Option C**: Force of gravity - This is not relevant in the horizontal oscillation of the needle. - **Option D**: All of the above factors - This is incorrect since only the horizontal component of the Earth's magnetic field is responsible for the restoring force. 5. **Conclusion**: The correct answer is that the restoring force originates mainly from the horizontal component of the Earth's magnetic field. ### Final Answer: The restoring force originates mainly from the horizontal component of the Earth's magnetic field. ---
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