This question is incomplete, the complete question is;
A loop of radius r = 3.0 cm is placed parallel to the xy-plane in a uniform magnetic field B = 0.75 Tˆk.
The resistance of the loop is 18 Ω. Starting at t = 0, the magnitude of the field decreases uniformly to zero in 0.15 seconds.
What is the magnitude of the electric current produced in the loop during that time?
Answer
a 2.1 mA
b 0.79 mA
c 1.7 mA
d 0.20 mA
e 3.9 mA
Answer: option (b) 0.79 mA is the correct answer
Step-by-step explanation:
Given that;
radius r = 3 cm = 0.03 m
Magnetic field B = 0.75
Resistance R = 18
time t = 0.15s
Area A = πr² = π(0.03)² = 0.002827 m²
we know that
Induced EMF ∈ = -BA / T
and ∈ is also = IR
so, IR = -BA/t
I = -BA / Rt
we substitute our values into the equation
I = [- (-0.75 × 0.002827)] / [18 × 0.15]
= 0.002120 / 2.7
= 0.0007851 A ≈ 0.00079 A ≈ 0.79 mA ( milliamperes )
Therefore option (b) 0.79 mA is the correct answer