Question

A perfectly conducting U-shaped rail is spanned by a rod which is able to slide without friction. The rod has a mass m =1 .2 kg and a resistanceR =2 .0?. The rod and rail sit in a uniform magnetic ?eld of magnitude B =0 .4 T, which is out of the page as shown in the ?gure below. The long sections of the rail are separated by a distance W =0 .25 m. Rod
W F
Part A
(a) With reference to Faraday’s law, explain two fundamentally di?erent ways in which an emf can be generated around the circuit created by the rod and the rail. (b) A constant force~ F is applied to the rod to move it to the right at a speed of v =2 .2ms 1. What is the magnitude of the induced emf, and the direction of the induced current in the circuit?
(c) At a later time, the force is suddenly removed. Give a qualitative description of the subsequent motion of the rod, and explain your reasoning.
Part B (Advanced)
Suppose the magnetic ?eld was replaced by a uniform electric ?eld, also pointing out of the page. A force is applied to the rod to move it along the rails. Would there be a magnetic ?eld generated? Explain why, or why not.

Answer 1