A U - shaped conducting frame is fixed in space. A conducting rod CD lies at rest on the smooth frame as shown. The frame is in a uniform magnetic field `B_0` which is perpendicular to be plane of the frame . At the time t = 0 , the magnitude of the magnetic field being to change with time t as, `B =B_0/(1+kt)` , where k is a positive constant . For no current to be ever induced in the frame the speed with which rod should be pulled starting from time t = 0 is (the rod CD should be moved such that its velocity must lie in the plane of frame and perpendicular to rod (CD)

Options

A. ak
B. bk
C. `a(1+kt)`
D. `b(1+kt)`

Answer

A