$A$ device which converts electrical energy into mechanical energy 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?

In an $A.C.$ generator,when the plane of the coil is perpendicular to the magnetic field:

$A$ simple electric motor has an armature resistance of $1 \,\Omega$ and runs from a d.c. source of $12 \,V$. It draws a current of $2 \,A$ when unloaded. When a certain load is connected to it,its speed reduces by $10 \%$ of its initial value. The current drawn by the loaded motor is ......... $A$

An electric motor operating on a $60\, V$ $dc$ supply draws a current of $10\, A$. If the efficiency of the motor is $50\%$,the resistance of its winding is.....$\Omega $

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