A wheel with 10 metallic spokes each 0.5 m long is rotated with a speed of 120 rev/min in a plane normal to the horizontal component of earth’s magnetic field `H_(E)` at a place. If `H_(E)` = 0.4 G at the place, what is the induced emf between the axle and the rim of the wheel? Note that 1 G = `10^(–4)` T.

Explanation

f= 120 rev/min= 2 rev/second,
B= 0.40 gauss `= 0.4 xx 10^(-4)T`, Area swepty, by each spoker per second, `A= pi r^(2)f`
Magnetic flux cut by each spoke per second, `(d phi_(B))/(dt)= BA = B pi r^(2)f`
Induced emf, `e= B pi r^(2)f` (numerically)
`e= 0.4 xx 10^(-4) xx (22)/(7) xx 0.5 xx 0.5 xx 2`
`e= 6.29 xx 10^(-5)` volt