Question
A current carrying rectangular loop PQRS is made of uniform wire. The length $PR = QS =5\,cm$ and $PQ = RS =100\,cm$. 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 RS in the two cases respectively $f_{ PQ }^{ I }: f_{ PQ }^{2 I }$ is :
