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 2I, the ratio of magnetic forces per unit length on wire PQ due to wire RS in the two cases respectively is: Image
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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 2I, the ratio of magnetic forces per unit length on wire PQ due to wire RS in the two cases respectively is: Image

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G1 Physics · Accepted Answer

Force per unit length between parallel current-carrying wires is proportional to I₁I₂. When the loop current changes from I to 2I, both interacting currents double, so force becomes four times. Ratio = 1:4.