# Homework Help: EMI qns help!

1. Jul 2, 2011

### 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

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. im not sure if the area will increase or decrease. and why?

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2. Jul 2, 2011

### Staff: Mentor

Re: ＥＭＩ　ｑｎｓ　ｈｅｌｐ！

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

3. Jul 2, 2011

### april_angela

Re: ＥＭＩ　ｑｎｓ　ｈｅｌｐ！

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

4. Jul 2, 2011

### Staff: Mentor

Re: ＥＭＩ　ｑｎｓ　ｈｅｌｐ！

Good. So how does that relate to this problem?

5. Jul 2, 2011

### april_angela

Re: ＥＭＩ　ｑｎｓ　ｈｅｌｐ！

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

6. Jul 2, 2011

### Staff: Mentor

Re: ＥＭＩ　ｑｎｓ　ｈｅｌｐ！

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

7. Jul 2, 2011

### april_angela

Re: ＥＭＩ　ｑｎｓ　ｈｅｌｐ！

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

8. Jul 2, 2011

### Staff: Mentor

Re: ＥＭＩ　ｑｎｓ　ｈｅｌｐ！

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

9. Jul 2, 2011

### april_angela

Re: ＥＭＩ　ｑｎｓ　ｈｅｌｐ！

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