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(B) The induced $e.m.f.$ $(e)$ in a dynamo armature is given by the formula $e = N B A \omega \sin(\omega t)$, where $N$ is the number of turns, $B$ i

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(B) The induced $e.m.f.$ $(e)$ in a dynamo armature is given by the formula $e = N B A \omega \sin(\omega t)$, where $N$ is the number of turns, $B$ is the magnetic field, $A$ is the area of the coil, and $\omega$ is the angular (rotational) velocity.From this relation, we can see that the induced $e.m.f.$ is directly proportional to the rotational velocity, i.e., $e \propto \omega$.If the rotational velocity $\omega$ is doubled $(2\omega)$, the induced $e.m.f.$ will also become two times the original value.

If the rotational velocity of a dynamo armature is doubled, then the induced $e.m.f.$ will become

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