A circular wire loop 53 cm in diameter has resistance 120 OHM and lies in a hori

Question

A circular wire loop 53 cm in diameter has resistance 120 OHM and lies in a horizontal plane. A uniform magnetic field points vertically downward, and in 25 ms it increases linearly from 5.0 mT to 55 mT. Find the magnetic flux through the loop at the beginning. Find the magnetic flux through the loop at the end of the 25-ms period. What's the loop current during this time? Express your answer with the appropriate units. Which way does this current flow? Select the correct answer and explanation. I is counterclockwise when viewed from above the loop because induced field is downward. I is clockwise when viewed from above the loop because induced field is upward. I is counterclockwise when viewed from above the loop because induced field is upward. I is clockwise when viewed from above the loop because induced field is downward.

Explanation / Answer

r = 26.5 cm = 0.265m
R = 120 ohm
t = 25*10^-3
Bf = 55*10^-3 T
Bi = 5*10^-3 T

flux change = A(Bf - Bi) = pi*0.265^2 *50*10^-3 = 0.011025
EMF = flux change/t = 0.441013 V

1. flux in begining = pi*0.265^2*5*10^-3 = 1.10*10^-3
2. Flux at the end = pi*0.265^2*55*10^-3 = 12.12 *10^-3
3. V = IR
I = 0.441013/120 = 3.675*10^-3 A
4. I is counterclockwise when viewed from above the loop because induced field is upward

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