Force on Current-Carrying Conductors
A current carrying rectangular loop PQRS is made of uniform wire. The length and . If ammeter current reading changes from I to , the ratio of magnetic forces per unit length on the wire due to wire in the two cases respectively is:

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Answer: (a)
- PQ and RS are identical branches in parallel, so each carries half the total current.
- Force per unit length .
- So the answer is (a) 1 : 4.