Question

A flat coil of radius 4 cm has 30 turns and a resistance of 0.15 Ω, and is placed on a horizontal table.

Initially, a uniform magnetic field of 0.75 T pointing upward (viewed from an observer above the table) passes through the coil. In 0.25 s, the magnitude of the magnetic field is changed to 0.35 T and the direction is completely reversed.

(a) Determine the direction of the induced current in the coil. 2%

Answer: ______________

Explain in detail:

(b) Find the average induced current in the loop. 3%

Answer: ___________

Answer 1

(a)

direction of the induced current in the coil = counterclockwise (from lenz's law)

according to lenz law, induced current oppose the changing flux.

point your thumb in upward decreasing field and curl your firgers.

Here the direction of curling is counterclockwise. so, the direction of current is CCW.

(b)

lnduced emf in the loop,

e = -N*d / dt

e = -N*(B*A*cos) / dt

e = -30*[(0.35 - (-0.75))*pi*0.04^2*cos180] / 0.25

e = 0.6635 V

average induced current in the loop,

i = e / R

i = 0.6635 / 0.15

i = 4.42 A