1 Marks Question

Question 11 Mark

The free electrons in a conducting wire are in constant thermal motion. If such a wire, carrying no current, is placed in a magnetic field, is there a magnetic force on each free electron? On the wire?

Answer

Yes, each electron experiences a force. But since the motion is random the net force on collective electrons is zero.

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Question 21 Mark

Can a charged particle be accelerated by a magnetic field? Can its speed be increased?

Answer

Yes (in circular path), No since magnetic field does no work.

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Question 31 Mark

Suppose a charged particle moves with a velocity v near a wire carrying an electric current. A magnetic force, therefore, acts on it. If the same particle is seen from a frame moving with velocity v in the same direction, the charge will be found at rest. Will the magnetic force become zero in this frame? Will the magnetic field become zero in this frame?

Answer

Current doesn't depend on reference frame as if electron comes to rest, protons moves in oppositive direction therefore the magnetic field will not become zero.
Since, the charged particle appears to be at rest therefore the force due to magnetic field becomes zero.

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Question 41 Mark

Will a current loop placed in a magnetic field always experience a zero force?

Answer

If the magnetic field is uniform in space. If it is non-uniform net force will not be always zero.

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Question 51 Mark

Is it possible for a current loop to stay without rotating in a uniform magnetic field? If yes, what should be the orientation of the loop?

Answer

Angle must be $\theta=0^\circ$ or 180^o between magnetic field and magnetic moment.

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