Electromotive force induced in a conducting rod

  • Thread starter DottZakapa
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Homework Statement:

Two long, parallel and perfectly conducting rails at a distance l = 50 cm from each other are placed in a homogeneous magnetic field with magnetic induction B = 2 mT, which is perpendicular to the rail plane. The rails are conductively connected at one point.
Electrical resistance of the connection is R = 5 Ω. A perfectly conducting rod slides on these rails with a constant speed v = 2 ms-1. Determine:
a) the electromotive force induced in the conducting rod, the value and direction of induced electric current in the closed part of the circuit,
b) the mechanical pulling force needed to keep the rod at the constant speed and mechanical powe

Relevant Equations:

electromotive force
Screen Shot 2019-09-12 at 11.35.53.png

i don't understand why in the solution of this exercise, the induced electromotive force / current is counterclockwise.
Shouldn't it be clockwise?
##emf=-\frac {d \Phi_B} {dt} ##
According to the picture the rod is moving upward, the magnetic flux (entering the page) is decreasing due to a reduction of the area, consequently the induced current will flow in such way that the magnetic field produced is in the same direction of the magnetic field that induced it. It would go counterclockwise only if the area was increasing which would imply an increase of magnetic flux, hence the magnetic field produced by the induced current will oppose it.
Isn't it?
 

Answers and Replies

  • #2
BvU
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I agree with you. The convention is that a cross is into the page (circle with center point is out of the page) and then ##\vec v \times \vec B ## points to the left.

Any indication in the solution (which solution?) that they have the red rod on the top of the picture, having passed the resistor ?
 

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