Q6.14 (e) Figure 6.20 shows a metal rod resting on the smooth rails
and positioned between the poles of a permanent magnet. The rails, the rod, and the magnetic field are in three mutually perpendicular directions. A galvanometer
connects the rails through a switch
. Length of the
,
, resistance of the closed loop containing the
. Assume the field to be uniform. Suppose K is open and the rod is moved with a speed of
in the direction shown. Give the polarity and magnitude of the induced emf. How much power is required (by an external agent) to keep the rod moving at the same speed
when
is closed? How much power is required when
is open?
The power from external sources is required to overcome the resisting force of
The velocity at which the rod moves is given as
The power is calculated as,
So, When key K is open, there is no current flow in the rod, thus no power is required.