Following figure shows a metal rod PQ resting on the smooth ralls AH and positioned between the poles of a permanent magnet. The rails, the rod and the magnetic field are in three mutual perpendicular directions. A galvanometer G connects the rails through a switch K. Length of the rod 15 cm, B 0.50 T, resistance of the closed loop containing the rod `9.0 mOmega`. Assume the field to be uniform.
What is the induced emf in the moving rod if the magnetic field is parallel to the rails instead of being perpendicular?

Explanation

Given, length of the rod `l=15cm=15xx10^(-2)m` Magnetic field `B=0.50T`
Resistance of the closed - loop containing the rod, `R=9mOmega=9xx10^(-3)Omega`
Velocity of rod `V=12" cm/s "12 xx 10^(-2) m//s.`
When the field is parallel to length of rails `theta-0^(@)`, induced emf `=e=BVl sin theta=0` `(therefore sin theta^(@)=0)`. In this situation, the moving rod will not cut the field lines so that flux change is zero and hence induced emf is zero.