Question

This problem explores how a current-carrying wire can be accelerated by a magnetic field. You will use the ideas of magnetic flux and the EMF due to change of flux through a loop. Note that there is an involved follow-up part that will be shown once you have found the answer to Part B.

A.) A conducting rod is free to slide on two parallel rails with negligible friction. At the right end of the rails, a voltage source of strength V in series with a resistor of resistance R makes a closed circuit together with the rails and the rod. The rails and the rod are taken to be perfect conductors. The rails extend to infinity on the left. The arrangement is shown in the figure.

There is a uniform magnetic field of magnitude B, pervading all space, perpendicular to the plane of rod and rails. The rod is released from rest, and it is observed that it accelerates to the left. In what direction does the magnetic field point? (CHOSE ONE)

- into the plane of the figure - out of the plane of the figure

B.) Assuming that the rails have no resistance, what is the most accurate qualitative description of the motion of the rod? (CHOSE ONE)

- The rod will accelerate but the magnitude of the acceleration will decrease with time; - the velocity of the rod will approach but never exceed a certain terminal velocity. - Under these idealized conditions the rod will experience constant acceleration and the velocity of the rod will increase indefinitely. - The rod will accelerate indefinitely with acceleration proportional to its (increasing)velocity.

Answer 1

a) the current is down along the rod, the force is towards left , so the magnetic field is out of page.

b) The rod will accelerate but the magnitude of the acceleration will decrease with time; the velocity of the rod will approach but never exceed a certainterminal velocity. - wrong because acceleration is zero at terminal velocity

Under these idealized conditions the rod will experience constant acceleration and the velocity of the rod will increase indefinitely.- No the accelerationincreases to maximum and then decreases so that the rod comes to rest.

The rod will accelerate indefinitely with acceleration proportional to its (increasing) velocity. - Correct.