The figure shows a bar moving to the right on two conducting rails. To make an induced current i in the direction indicated, a constant magnetic field in region A should be in what direction?
A) Right
B) Left
C) Into the page
D) Out of the page
E) Impossible, cannot be done with a constant magnetic field

Question

The figure shows a bar moving to the right on two conducting rails. To make an induced current i in the direction indicated, a constant magnetic field in region A should be in what direction? 
A) Right 
B) Left 
C) Into the page 
D) Out of the page 
E) Impossible, cannot be done with a constant magnetic field

Quizplus · Accepted Answer

According to Lenz's Law, the induced current will be in a direction that opposes the change in magnetic flux. As the bar moves to the right, the magnetic flux through the loop formed by the bar and the rails is decreasing. Therefore, the induced current should produce a magnetic field into the page, which would oppose the original magnetic field and slow down the bar. This can be achieved with a constant magnetic field in region A that is also into the page.

The Figure Shows a Bar Moving to the Right on Two