Solution 1

Calculate the EMF of the dc motor.

Here, i8s voltage, back emf, armature current, is armature resistance.

Substitute for , for and for .

Calculate the torque.

Here, represent the torque; represent the number of turn.

Substitute for , for and for .

Therefore, torque developed armature is

Solution 2.

The series winding of a differential compound motor opposes its shunt winding and thus there is decrease in resultant flux if the load is increased. This motor runs at very high speed than as a shunt motor. The heavier is the load faster the motor will run and this can be more dangerous as this may cause damage in motor. At overload the motor run as a

Solution3.

The direction of force in a current carrying conductor can be obtained with the help of Fleming’s right hand rule. According to this rule the thumb represents the direction of force, fore-finger represents the magnetic field and middle finger represents the direction of current. The expression for this rule be written as follows:

Here, represents the force acting on conductor, represents the magnetic field

intensity, is the current flow in the conductor, is the length of conductor. Among these the force, magnetic field intensity and current are vector quantities as they have some direction.

Solution 4

When a DC motor is connected across an AC supply then in DC motor no proper magnetic field will produce due to change of phases in supply. It will also cause sparkling the brushes in motor and also eddy current will increase rapidly that cause heat in motor and the motor will burn up.

Therefore the motor will burn up due to heat produced from eddy current losses.

Solution 5

The given statement is true. The MOSFETs consists of internally connected antiparallel diodes and that is why they cannot withstand the reverse voltage. Hence, they cannot be used as current source inverter but can be driven as a voltage source inverter.