Counter EMF and Motor Power

The video tutorial explains the functioning of a DC motor, focusing on internal resistance and counter EMF. It covers how to calculate the current when the motor is starting up and at full speed using Ohm's law. The relationship between counter EMF and angular speed is discussed, with examples of calculating EMF at different RPMs. The tutorial also demonstrates how to calculate the current and power dissipation in the motor, concluding with a review of key formulas and concepts.

What is the current in a DC motor with an internal resistance of 10 ohms when connected to a 12V battery and the counter EMF is 0V?

• 1.2 A

• 0.8 A

• 0.5 A

• 1.0 A

How does the counter EMF change as the speed of a DC motor increases?

• It decreases

• It remains constant

• It increases

• It fluctuates

If a DC motor has a counter EMF of 14 volts at 2100 RPM, what is the counter EMF at 3500 RPM?

• 17.0 V

• 21.0 V

• 23.3 V

• 19.5 V

What is the counter EMF of a DC motor with a 5 ohm internal resistance and a current of 2 amps at 300 RPM?

• 5 V

• 4 V

• 3 V

• 2 V

How do you calculate the counter EMF of a motor using the formula V - IR = EMF?

• Divide V by IR

• Subtract IR from V

• Add IR to V

• Multiply IR by V

What is the counter EMF of a motor at 1200 RPM if it was 2 volts at 300 RPM?

• 10 V

• 8 V

• 4 V

• 6 V

What is the current flowing through a motor with a counter EMF of 8 volts, a 12V battery, and 5 ohms resistance?

• 0.6 A

• 1.0 A

• 1.2 A

• 0.8 A

How much power is dissipated by a motor with a current of 0.8 amps and an internal resistance of 5 ohms?

• 3.2 W

• 4.0 W

• 2.5 W

• 3.5 W

Which formula is used to calculate the power dissipated by a resistor?

• I^2R

• VI

• V^2/R

• IR^2

What happens to the counter EMF as the angular speed of a motor increases?

• It increases

• It becomes zero

• It remains constant

• It decreases