A loop of radius r = 3 cm is placed parallel to the xy-plane in a uniform magnetic field = (0.75 T) . The resistance of the loop is R = 18 Ω. Starting at t = 0, the magnitude of the field decreases uniformly to B = 0 in 0.15 seconds. What is the magnitude of the electric current produced in the loop during that time?

i = 0.00077A

Explanation:

Given:

loop radius, r = 3.0 cm = 0.03 m

Area, A = π x r² = π x 0.03² = 0.0028 m²

Magnetic Field, B = 0.75 T

Loop resistance, R = 18 Ω

time, t = 0.15 seconds

Now,

the induced emf is given as:

EMF = - BA/t 1

Likewise,

EMF = iR2

Equate 1 and 2

iR = - BA/t

i = - BA/tR

i = 0.75×0.0028/0.15×18

i = 0.0021/2.7

i = 0.00077A

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the minimum amperage that the current in this wire would have to have so that its weight is completely supported by the magnetic force due to earth's field, assuming that no other forces except gravity act on it