The armature of a $DC$ motor has $20\,\Omega$ resistance. It draws a current of $1.5\,A$ when run by a $220\,V$ $DC$ supply. The value of the back $EMF$ induced in it will be......$V$

$A$ generator has an armature resistance of $0.1 \, \Omega$ and develops an induced emf of $120 \, V$ when driven at its rated speed. Its terminal voltage when a current of $50 \, A$ is being drawn is ................. $V$.

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

The output of a dynamo using a split-ring commutator is

An electric fan operates on the principle of which of the following?

Armature current in a $DC$ motor will be maximum when: