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A metal bar of mass m slides without friction over two rails a distance D apart in the region that has a uniform magnetic field of magnitude B0 and direction perpendicular to the rails (see below). The two rails are connected at one end to a resistor whose resistance is much larger than the resistance of the rails and the bar. The bar is given an initial speed of v0. It is found to slow down.
How far does the bar go before coming to rest?

Assume that the magnetic field of the induced current is negligible compared to B0.
(Source: OpenStax Physics Volume 2)

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Mark Yourself Question
  1. Grab a piece of paper and try this problem yourself.
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  3. View the solution and report whether you got it right or wrong.
Two conducting wires are located in a uniform magnetic field BB pointing directly out of the page. One wire is along the x-axis. The other wire has a parabolic form, of heighty=αx2y=\alpha x^2 above the x-axis.
A vertical bar with resistanceRR (parallel to the y-axis) with constant speed VV moves along the first two wires. It starts at xxand moves to the left, towards the origin.
a) What is the current in the bar?
b) What is the direction of the induced current in the vertical bar (up or down)?


The accompanying figure shows a single-turn rectangular coil that has a resistance of 2.0 Ω. The magnetic field at all points inside the coil varies according to B = B0e−αt, where B0 = 0.25 T and α = 200 Hz.

What is the current induced in the coil at (a) t = 0.001 s, (b) 0.1 s, (c) 1.0 s? Also, what is the direction of the induced current (same for all three values)?

(Source: OpenStax Physics Volume 2)