Question

Four wires each of length $2m$ are bent into four loops $P,Q,R$, and $S$ and then suspended into a uniform magnetic field and same current is passed in each loop. The correct statement is

• A. couple on loop $P$ will be highest
• B. couple on loop $Q$ will be highest
• C. couple on loop $R$ will be highest
• D. couple on loop $S$ will be highest

Answer 1

Answer: (D)

couple on loop $S$ will be highest

for a given perimeter , a circle has the largest area So,
$\overrightarrow{\tau }=\overrightarrow{M}\times \overrightarrow{B}$
$\tau =InAB$
So, $\tau \alpha A$
So, area is greater leads to more torque
So, loop $s$ will have highest torque (couple).