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Electric Generators and Back emf

Electric Generators and Back emf

Assessment

Presentation

Physics

11th - 12th Grade

Hard

Created by

Rachel Wampler

Used 1+ times

FREE Resource

7 Slides • 1 Question

1

Electric Generators and Back emf

By Rachel Wampler

2

Electric Generators

  • A loop of wire is rotated in a magnetic field.

  • Since the angle between the loop and the B-field is changing, the flux is changing.

  • Since the magnetic flux is changing an emf is induced.​

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3

Electric Generators

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Electric Generators

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Where:

N = number of loops

B = magnetic field

A = area of each loop

​ω = angular velocity = 2πf (f = frequency)

t = time in seconds​

emf Produced in a Rotating Planar Coil

6

AC Generators

  • According to Lenz's Law, the current will flow the one direction when the angle is increasing and it will flow the opposite direction when the angle is decreasing.

  • These generators are often called alternating current generators.

7

Multiple Choice

You have made a simple generator to power a TV. The armature is attached the rear axle of a stationary bike. For every time you peddle, the rear axel turns 10 times. Your TV needs a Vrms of 110V to operate. If the B-field is 0.2 T, each loop is a circle with r = 3 cm, and you can comfortably peddle 3 times a second; how many loops must you have in your generator so that you can watch TV while you exercise?

1

26 loops

2

4860 loops

3

155 loops

4

1460 loops

8

Back emf

  • When a coils is turned in a B-field an emf is produced

  • If an electric motor is running, its coil is turning in a B-field

  • By Lenz's Law, this emf will oppose the emf used to turn the motor, called back emf.

  • It will reduce the voltage across the motor and cause it to draw less current (Remember, V=IR)

  • The back emf is proportional to the speed, so when the motor starts it draws max I, but as it speeds up the I decreases.​

Electric Generators and Back emf

By Rachel Wampler

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