A wheel with ten metallic spokes each `0.50 m` long is rotated with a speed of `120 rev//min` in a plane normal to the earth's magnetic field at the place. If the magnitude of the field is `0.4` gauss, the induced e.m.f. between the axle and the rim of the wheel is equal to

Explanation

Induced emf = `(1//2) omega B R^(2)`
`= (1//2)xx4pixx0.4xx10^(–4)xx(0.5)^(2)`
`= 6.28 × 10^(–5) V`
The number of spokes is immaterial because the emf’s across the spokes are in parallel.