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A loop of area 1 m 2 is placed in a magnetic field B = 2T, such that plane of the loop is parallel to the magnetic field. If the loop is rotated by 180°, the amount of net charge passing through any point of loop, if its resistance is 10 Q is (a) 0.4 C (b) 0.2 C (c) 0.8 C (d) 0 C

I am confused between options a and d. The flux change when rotated 180° will be 0 so emf will be 0. But then if we look at the position when it has rotated 90° then emf is not 0 so some charge flows. Which logic is correct?

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d) is correct.

Yes, when it was rotated by 90° , some +emf was induced, which caused charge to flow in certain direction as $d\frac{\phi}{dt}$ = +ve .

when it was rotated by next 90° , -emf was induced, which caused charge to flow in opposite direction as $d\frac{\phi}{dt}$ = -ve .

So, net current is 0 which gives 0 flow of charge.

Edit: Question asks for net charge flow which is 0.

If it were only charge flow, you will consider it 2Q.

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  • $\begingroup$ This is where i am stuck: if q charge flows in one direction and then q charge flows in opposite direction then while calculating amount of charge flowing shouldnt we just add the charges instead of considering their direction of flow. Like if 2C charge flows in clockwise sense and then another 2C charge flows in anticlockwise direction then the amount of charge flown is 4C or 0C? $\endgroup$ Commented Apr 11, 2016 at 11:41
  • $\begingroup$ Done it brother $\endgroup$ Commented Apr 11, 2016 at 14:22

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