A current carrying rectangular loop $PQRS$ is made of uniform wire. The length $PR=QS=5 \mathrm{cm} \text{and} PQ=RS=100 \mathrm{cm}$. 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 $\left(f_{PQ}^I:f_{PQ}^{2I}\right)$ is: