Q. A conducting straight wire PQ of length l is fixed along a diameter of a non-conducting ring as shown in the figure. The ring is given a pure rolling motion on a horizontal surface such that its centre of mass has a velocity v. There exists a uniform horizontal magnetic field B in horizontal direction perpendicular to the plane of ring. The magnitude of induced emf in the wire PQ at the position shown in the figure will be
(a) Bvl
(b) 2Bvl
(c)3Bvl/2
(d) zero
Ans: (a)
Sol: induced emf in the wire PQ is
$\displaystyle e = B v (PQ)$
$ \displaystyle e = B v l $