A current carrying rectangular loop \( PQRS \) is made of uniform wire. The length \( PR = QS = 5 \, \text{cm} \) and \( PQ = RS = 100 \, \text{cm} \). If ammeter current reading changes from \( I \) to \( 2I \), the ratio of magnetic forces per unit length on the wire \( PQ \) due to wire \( RS \) in the two cases respectively \( ( f_{PQ}^{I} : f_{PQ}^{2I} ) \) is :
