A coil of 150 turns and area is mounted on an axle so that it can rotate in a uniform…

PHYSICS · Subjective · A Level · Physics · Fields and their consequences · Fields and their consequences

Problem

A coil of 150 turns and area

0.050\,\text{m}^2

is mounted on an axle so that it can rotate in a uniform magnetic field of

0.60\,\text{T}

. Starting from rest at

t=0

, the coil is given a constant angular acceleration so that its angular speed varies with time as

\omega = b t

, where

b = 20\,\text{rad}\,\text{s}^{-2}

. The plane of the coil is perpendicular to the magnetic field at

t=0

. (i) Derive an expression for the instantaneous emf induced in the coil as a function of time for

t>0

. (ii) Calculate the magnitude of the induced emf at

t = 0.20\,\text{s}

. (iii) Determine the smallest positive time (other than

t=0

) at which the emf becomes zero again.