Question

A square loop of side $5\, cm$ enters a magnetic field with $1\, cm\, s ^{-1}$. The front edge enters the magnetic field at $t=0$ then which graph best depicts emf?

• A.
• B.
• C.
• D.

Answer 1

Answer: (C)

When loop is entering in the field, magnetic flux linked with the loop increases so induced emf in it
$e=B v l=0.6 \times 10^{-2} \times 5 \times 10^{-2}=3 \times 10^{-4} V$ (Negative)
When loop completely enters in the field (after $5\, s$) flux linked with the loop remains constant, so $e=0$.
After $15\, s$, loop begins to exit out, so linked magnetic flux decreases and hence induced emf $e=3 \times 10^{-4} V$ (Positive).