Counter emf generated in a motor at full speed

In summary, counter electromotive force (emf) is a voltage that opposes the flow of current in a circuit, generated when a changing magnetic field induces an electric current in a conductor. In motors, it is important for regulating the motor's speed and is generated by the rotation of the rotor. If not properly controlled, it can affect the motor's performance by causing it to run too slow or too fast. To manage counter emf in a motor at full speed, a higher voltage power supply, motor controllers, and proper maintenance can be used.
  • #1
lloyd21
112
0

Homework Statement


An electric motor draws 20.0 A of current when first switched on. The motors windings have a resistance of 5.0 ohm. Once the motor is up to full speed it draws only 4.4 A of current. Calculate the counter emf generated in the motor at full speed

Homework Equations


I = V/R
V=IR

The Attempt at a Solution


R = 5.0 ohm
A1 = 20.0 A
A2= 4.4 A n

1. (20A)(5.0ohm) = 100 V

2. (4.4A)(5.0ohm) = 22V

3. 100V - 22V = 78V

Im told I am missing some "change", however I think this is correct, it is change in voltage?
 
Physics news on Phys.org
  • #2
Looks fine to me.
 

What is counter emf?

Counter electromotive force (emf) is a voltage that opposes the flow of current in a circuit. It is created when a changing magnetic field induces an electric current in a conductor, causing a voltage to be generated in the opposite direction.

Why is counter emf important in motors?

In motors, counter emf plays a crucial role in regulating the speed of the motor. As the motor rotates, it generates counter emf that opposes the applied voltage, thus reducing the overall current and preventing the motor from running at dangerously high speeds.

How is counter emf generated in a motor?

Counter emf is generated in a motor when the rotation of the rotor creates a changing magnetic field that induces an electric current in the stator windings. This current then produces a magnetic field that opposes the original field, thus generating counter emf.

Does counter emf affect the performance of a motor?

Yes, counter emf can affect the performance of a motor if it is not properly controlled. If the counter emf is too high, it can cause the motor to run slower than desired or even stall. On the other hand, if the counter emf is too low, it can cause the motor to run at dangerously high speeds.

How can counter emf be managed in a motor at full speed?

To manage counter emf in a motor at full speed, a power supply with a higher voltage can be used to compensate for the counter emf and maintain the desired speed. Additionally, motor controllers can be used to regulate the current and keep it at a safe level. Proper maintenance and monitoring of the motor's components can also help manage counter emf.

Similar threads

Calculating EMF and Load Resistance for a Motor
    • Introductory Physics Homework Help
Replies
11
Views
1K
Internal Resistance of a Car Battery
    • Introductory Physics Homework Help
Replies
8
Views
12K
Solving Resistor Circuit Homework: DC Motor, Rf, Rr, E, If, Ir, Pth
    • Introductory Physics Homework Help
Replies
13
Views
8K
Help understanding 'back emf'
    • Introductory Physics Homework Help
Replies
3
Views
3K
Engineering Solve Motor Coil Current at Startup & Full Speed
    • Engineering and Comp Sci Homework Help
Replies
4
Views
868
DC motor. Calculate the current
    • Introductory Physics Homework Help
Replies
1
Views
1K
Current drawn by a motor operating at half speed
    • Introductory Physics Homework Help
Replies
4
Views
2K
Understanding Back EMF in DC Motors
    • Introductory Physics Homework Help
Replies
16
Views
2K
What Is the Voltage Across the Resistor in an LC Circuit with Given Parameters?
    • Introductory Physics Homework Help
Replies
3
Views
8K
Engineering Calculating EMF and Motor Speed for a Compound Wound D.C. Motor
    • Engineering and Comp Sci Homework Help
Replies
3
Views
2K

Hot Threads

Recent Insights

Back
Top