# Relationship between potential and induced emf?

## Homework Statement

[PLAIN]http://img220.imageshack.us/img220/2589/44045733.png [Broken]

Semicircular wire MN of diameter L moves with speed v perpendicularly through a uniform magnetic field of strength B.

1. Find the magnitude of the induced emf generated between M and N.
2. State whether M or N is at a higher potential.

E = BLv

## The Attempt at a Solution

1. Given answer: Induced emf = BLv

However, I was wondering if you can use that equation even if it's not a closed circuit?
In the semicircular wire, there shouldn't be magnetic flux linkage. And even if there was, there is no change in magnetic flux linkage.

2. N is at a higher potential

There is opposing force that resists the motion of the wire ( is this reason correct?), which, by Fleming's left hand rule, results in an induced current (if the circuit were to be closed) flowing from M to N. Thus, N is at higher potential as a result of the induced "current".

However, I know that current flows from higher potential to lower potential. So is it right to say that in the case of an induced current, if it flows from M to N, N is at a higher potential?

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However, I was wondering if you can use that equation even if it's not a closed circuit?
Sure, you can, you have to.
Just be careful what "length" is.

If it was a closed circuit of zero resistance, there would be no voltage at all.
V=RI, R=0, so V=0 (for closed loops of zero resistance)

However, I know that current flows from higher potential to lower potential. So is it right to say that in the case of an induced current, if it flows from M to N, N is at a higher potential?
Pay attention to the charge sign.

There is opposing force that resists the motion of the wire
No there's no opposing force.

No there's no opposing force.
Then how is there an induced emf?

[PLAIN]http://img207.imageshack.us/img207/5853/93128344.png [Broken]

Do you take "Force" to be in direction of the velocity?

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i know the thread is old but i have a question
what shall we take as a length to calculate E, the length πr of the arc or the length 2r of the line segment and why?
thanks a lot