A wooden stick of length 3L is rotated about an end with constant angular velocity w (omega) in a uniform magnetict field B of perpendicular to the plane of motion. If the upper one-third of its length is coated with copper, the potential difference across the whole length of sticks?

potential difference will be due to motion of one third part of length...

change in area in 1 revolution, ds = pi(3L)²-pi(2L)² =5piL²       

angle bw magnetic field & area vector is 0 ..

flux passing through the one third part of length over 1 revolution is

@ = Bdscos0        (flux)

@ = Bds

e = d@/dt = Bds/dt =B5piL²/T

T=2pi/W

e = B5L²W/2