1) The flux through a loop of wire changes uniformly from + 47 Wb to -17 Wb in 1

ID: 1344794 • Letter: 1

Question

1) The flux through a loop of wire changes uniformly from + 47 Wb to -17 Wb in 1.9 ms .

a-What is the average induced emf in the loop?

b-If you wanted to double the average induced emf by changing only the final flux value, what would it be?

2) A 240-V dc motor has an armature whose resistance is 1.90 . When running at its operating speed, it draws a current of 13.0 A .

Part A

What is the back emf of the motor when it is operating normally?

Part B

What is the starting current? (Assume that there is no additional resistance in the circuit.)

Part C

What series resistance would be required to limit the starting current to 30.0 A ?

(1)

the fromula for average induced emf in the loop is

e =- d pi/ dt

= -(- 17 Wb - 47 Wb)/ 1.9 * 10 ^-3 s

=33.68 * 10 ^3 V

(b)

2e = - ( final flux - initial flux)/ time

2 ( 33.68* 10 ^3 V) = - ( final flux - 47 Wb)/1.9 * 10 ^-3 s

final flux = 2 ( 33.68* 10 ^3 V)( 1.9 * 10 ^-3 s)- 47 Wb

=-80.98 Wb

As per guide lines i did first question

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