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Question
A fan of metal blades of length 0.4 m rotates normal to a magnetic field of 4 x 10-3 T. If the induced emf between the centre and edge of the blade is 0.02 V, determine the rate of rotation of the blade.
Solution
Length of the metal blade, l = 0.4 m
Magnetic field, B = 4 x 10-3 T
Induced emf, e = 0.02 V
Rotational area of the blade, A = πr² = 3.14 x (0.4)² = 0.5024 m²
Induced emf in rotational of the coil, e = NBA ω sin θ
ω = `"e"/("NBA" sin theta)` ....[N = 1, θ = 90°, sin 90° = 1]
ω = `0.02/(1 xx 4 xx 106-3 xx 0.5024 xx sin 90^circ)`
`= 0.02/(2.0096 xx 10^-3)`
= 9.95222 x 10-3 x 103
= 9.95 revolutions/second
Rate of rotational of the blade, ω = 9.95 revolutions/second
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