Magnetism and the Effect on a Freely Hung Loop

[april_angela]

Fig.35 shows a light and flexible conducting loop X freely hung on a smooth horizontal rail. A
bar magnet PQ approaches the loop from the right. Which one of the following descriptions
about this process is correct?



A If P is a N-pole, the loop will be repelled to the left and its area will increase slightly.
B If P is a S-pole, the loop will be attracted to the right and its area will decrease slightly.
C No matter whether P is a N-pole or a S-pole, the loop will be repelled to the left and its area
will increase slightly.
D No matter whether P is a N-pole or a S-pole, the loop will be repelled to the left and its area
will decrease slightly.

can anyone help me with this qns? I've attached the diagram alrdy. I am not sure if the area will increase or decrease. and why?

 

[Doc Al]

Hint: If you have two current-carrying wires next to each other, do they attract or repel? Under what conditions?

 

[april_angela]

attract when the current flowing in the same direction;vice versa?

 

[Doc Al]

attract when the current flowing in the same direction;vice versa?

Good. So how does that relate to this problem?

 

[april_angela]

if the current repels the area increase? current attract area decrease? but idk how to relate to tis qns

 

[Doc Al]

Consider the induced current in the loop as the magnetic flux through the loop changes.

 

[april_angela]

the induced current will be in the direction to oppose the motion. - repel the approaching magnet. means area increase?

 

[Doc Al]

the induced current will be in the direction to oppose the motion. - repel the approaching magnet.

Good.

means area increase?

Yes, but why? (Not for the reason above.)

 

[april_angela]

if it repels the magnet. the area of the loop will widen and increase as if they are like straight conductors