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JAMB Physics 2007 Question 24

Question 24

Magnetism

Two long parallel wires X and Y carry currents 3A and 5A respectively. If the force experienced per unit length by X is 5 × 10−5 N, the force per unit length experienced by wire Y is

  1. A.5 × 10−4 N.
  2. B.3 × 10−6 N.
  3. C.3 × 10−5 N.
  4. D.5 × 10−5 N.
Show the answer and explanation

Answer: D (5 × 10−5 N.)

Explanation

The force per unit length between two wires is μ0IXIY/2πr, the same expression for both wires (Newton's third law). So Y feels the same 5 × 10−5 N per metre.