Counter emf generated in a motor at full speed

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SUMMARY

The discussion centers on calculating the counter electromotive force (emf) generated in an electric motor at full speed. The motor initially draws 20.0 A with a winding resistance of 5.0 ohms, resulting in an initial voltage of 100 V. At full speed, the current drops to 4.4 A, yielding a voltage of 22 V. The counter emf is calculated as 78 V, derived from the difference between the initial voltage and the voltage at full speed.

PREREQUISITES
  • Understanding of Ohm's Law (V = IR)
  • Basic knowledge of electric motor operation
  • Familiarity with the concept of counter electromotive force (emf)
  • Ability to perform calculations involving current and resistance
NEXT STEPS
  • Study the principles of electric motor efficiency and performance
  • Learn about the effects of load on motor current draw
  • Explore advanced topics in electromagnetic theory related to motors
  • Investigate methods for measuring counter emf in practical applications
USEFUL FOR

Electrical engineers, students studying motor dynamics, and anyone involved in the design or analysis of electric motor systems will benefit from this discussion.

lloyd21
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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?
 
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