In an $AC$ generator,the ends of the coil are connected to

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

$A$ rectangular coil of a simple $A.C.$ generator rotates about one of its diameters with a constant angular frequency in the presence of a uniform magnetic field. The direction of the induced current reverses for the third time after how many rotations of the coil?

Assertion : An electric motor will have maximum efficiency when back $emf$ becomes equal to half of applied $emf$.
Reason : Efficiency of electric motor depends only on magnitude of back $emf$.

The back emf in a $DC$ motor is maximum when,

$A$ motor having an armature of resistance $2\,\Omega$ is designed to operate at $220\,V$ mains. At full speed,it develops a back $e.m.f.$ of $210\,V$. When the motor is running at full speed,the current in the armature is: (in $,A$)