Relationship between potential and induced emf?

[Yoriko]

Homework Statement

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

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.

Homework Equations

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?

 

[Quinzio]

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.

 

[Yoriko]

No there's no opposing force.

Then how is there an induced emf?

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

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

 

[alkmini]

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