JEE Main · 2005 · 08 May 2005 · Offline · Magnetic Effects of Current

Two thin, long parallel wires separated by a distance '

d

' carry a current of '

i

A

in the same direction. They will

(A)attract each other with a force of $μ_{0} i^{2} / (2 π d)$ ✓ Correct
(B)repel each other with a force of $μ_{0} I^{2} / (2 π d)$
(C)attract each other with a force of $μ_{0} i^{2} (2 π d^{2})$
(D)repel each other with a force of $μ_{0} i^{2} / (2 π d^{2})$

Answer: (A)

Solution

Two long parallel wires carrying current the same way attract one another, each lying in the magnetic field of the other. The force per unit length is

\frac{μ _{0} i _{1} i _{2}}{2 π d}

, which for equal currents

i

becomes

\frac{μ _{0} i ^{2}}{2 π d}

, an attractive force.

JEE Main · 2005 · 08 May 2005 · Offline · Single correct option

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