Question

A current carrying rectangular loop $P Q R S$ is made of uniform wire The length $P R=Q S=5 \,cm$ and $P Q=R S=100\, cm$ If ammeter current reading changes from $I$ to $2 I$, the ratio of magnetic forces per unit length on the wire $P Q$ due to wire $R S$ in the two cases respectively $\left(f_{P Q}^I: f_{P Q}^{2 I}\right)$ is:

• A. $1: 5$
• B. $1: 3$
• C. $1: 2$
• D. $1: 4$

Answer 1

Answer: (D)

$1: 4$

Answer 2

F∝I1​I2​

F1​:F2I​=1:4

Therefore, The correct answer is option (D): 1:4