Q. A square loop of wire, side length 10 cm is placed at angle of 45${^\circ}$ with a magnetic field that changes uniformly from 0.1 T to zero in 0.7 s. The induced current in the loop (its resistance is 1 $\Omega)$is

A) 1.0 mA
B) 2.5 mA
C) 3.5 mA
D) 4.0 mA
Explanation

(a) Initial magnetic flux linked with the loop
$\phi = B_{1}A_{1}\cos\phi$
$\ \ \ \ = 0.1 \times \left( 10 \times 10^{- 2} \right)^{2}\cos{45{^\circ}}$
$\ \ \ \ = \ \frac{0.1 \times 10^{- 2} \times 1}{\sqrt{2}} = \frac{10^{- 3}}{\sqrt{2}}$
Final magnetic flux linked with the loop,$\phi_{2} = 2$
Now, induced emf in the loop ,$e = \frac{- \ d\phi}{dt}$
$\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ = \ \frac{- \left\lbrack \frac{10^{- 3}}{\sqrt{2}} \right\rbrack}{0.7} = 10^{- 3}V$
$\therefore$ Induced current =$\frac{e}{R} = \frac{10^{- 3}}{1} = 1\ mA$

Dr. Abubacker
Reviewed by Dr. Abubacker

Physics Educator & NEET/JEE Specialist

Ph.D. in Physics with 19+ years of teaching experience.