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So, the back emf is directly proportional to speed. Hence, when the speed of a DC shunt motor is increased, then the back emf of the motor will increase.

## When the speed of DC motor is increased the speed of DC motor is increased?

(3) we can say, speed is inversely proportional to armature current. Thus, when the speed of the dc motor is increased, the armature current will decrease. So, the correct answer is “Option B”.

## What will happen to torque if back emf and speed of the DC motor is doubled?

What will happen to torque if back emf and speed of the DC motor is doubled? Explanation: Torque depends on armature current, so as long as armature current remains constant torque will not change. Speed depends directly with back emf thus, it will definitely become double when back emf is doubled.

## What will be the effect on the speed of a shunt DC motor if the field current decreases?

Magnetic flux in turn is related to field current by the magnetisation characteristics. Hence speed of DC Shunt motor increases with decrease in field current.

## What will happen if the speed circuit of a DC motor is opened for a shunt motor?

Answer: n d.c shunt motor if field winding supply is removed the motor back emf will drop to zero, hence the armature will draw more current to make up the emf. this results in blowing up of fuse. In dc series motor the motor will go to infinite speed (theoretically) as flux is inversely proportional to the speed…

## What will happen if the back emf of a DC motor vanishes suddenly *?

Detailed Solution. If back emf of a dc motor vanishes suddenly, motor circuit will try to retain back emf by drawing more current from supply. As the back emf vanishes zero, the whole supply voltage appears across armature and heavy current flows.

## What will happen to a DC motor if its back emf is equal to the supply voltage?

As the back emf depends on the current their value also decreases. The magnitude of the back EMF is nearly equal to the supply voltage. If the sudden load is applied to the motor, the motor becomes slow down. As the speed of the motor decreases, the magnitude of their back emf also falls down.

## What is the action of the induced emf in a running DC motor?

When the armature of a DC motor rotates under the influence of the driving torque, the armature conductors move through the magnetic field and hence emf is induced in them as in a generator. The induced emf acts in opposite direction to the applied voltage V (Lenz’s law) and is known as Back EMF or Counter EMF (Eb).

## When a motor is just started back emf is almost?

Back emf is the generator output of a motor, and so it is proportional to the motor’s angular velocity ω. It is zero when the motor is first turned on, meaning that the coil receives the full driving voltage and the motor draws maximum current when it is on but not turning.

## Which determines the polarity of induced emf in DC shunt generator?

The polarity of induced emf depends upon the direction of the magnetic field and the direction of rotation. … In a motor, the induced emf is called Back Emf (E_{b}) because it acts opposite to the supply voltage.

## Why is the speed of DC shunt motor dependent on back EMF?

In the case of DC motors Speed ∝ Back emf(Eb)/flux(φ). The field winding is connected across the armature. The resistance offered by the field is constant so the current is constant. … Therefore the speed of the DC shunt motor depends on the back EMF.

## What is back EMF in a DC motor?

back EMF in Electrical Engineering

Back EMF is the system in the coil of an electric motor that opposes the current flowing through the coil, when the armature rotates. When the speed varies, the winding characteristics may fluctuate, resulting in variation of back EMF.

## Does the speed of a shunt motor increase or decrease when the armature current increases?

The change in armature current and torque on supplying load is graphically shown below. This increase in the amount of torque increases the speed and thus compensating for the speed loss on loading. Thus the final speed characteristic of a DC shunt motor, looks like.

## What will happen to the speed of a DC motor when its flux approaches zero?

Therefore, by increasing or decreasing Vwinding, the speed of DC motors increases or decreases respectively. And by increasing or decreasing flux, the speed of the DC motor decreases or increases respectively. Hence, when flux approaches zero, the speed of the motor approaches infinity.

## What will happen to the speed of DC shunt motor if the field suddenly opens and running at light load?

If field winding is disconnected accidentally, the speed would dangerously increase in order to maintain the back emf of the motor. For a constant back emf, flux is inversely proportional to the speed of the motor.

## What will happen if the direction of current at the terminals of a DC motor is reversed?

When both (the direction of the field as well as that of armature current) are reversed the direction of rotation will not change. So in the case of DC shunt motor, if the supply terminals are interchanged, there is no change in the direction of rotation.