Question

Four wires each of length 2.0 m are bent into four loops P, Q, R and S and then suspended into uniform magnetic field which is from left to right. Same current is passed in each loop. Which of the following statement is correct ?

• A. Couple on loop P will be the highest
• B. Couple on loop Q will be the highest
• C. Couple on loop R will be the highest
• D. Couple on loop S will be the highest

Answer 1

The correct option is D Couple on loop S will be the highest

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