A uniform magnetic field is restricted within a region of radius r. The magnetic field changes with time at a rate $\dfrac{d\overrightarrow{B}}{dt}$. Loop 1 of radius R > r encloses the region r and loop 2 of radius R is outside the region of magnetic field as shown in the figure below. Then the e.m.f. generated is
$–\dfrac{\text{d}\overrightarrow{B}}{\text{d}t}\pi r^2$ in loop 1 and zero in loop 2
zero in loop 1 and zero in loop 2
$–\dfrac{\text{d}\overrightarrow{B}}{\text{d}t}\pi r^2$ in loop 1 and $–\dfrac{\text{d}\overrightarrow{B}}{\text{d}t}\pi r^2$ in loop 2
$–\dfrac{\text{d}\overrightarrow{B}}{\text{d}t}\pi R^2$ in loop 1 and zero in loop 2
Explanation:
$e = – \dfrac{\text{d}\phi}{\text{d}t}= –\dfrac{\text{d}}{\text{d}t}{\pi r^2B} = – \pi r^2\dfrac{\text{d}B}{\text{d}t}$ in loop 1 & zero in loop 2.