JEE Main · 2004 · 24 Apr 2004 · Offline · Magnetic Effects of Current

Two long conductors, separated by a distance

d

carry current

I_{1}

and

I_{2}

in the same direction. They exert a force F on each other. Now the current in one of them increased to two times and its direction reversed. The distance is also increased to 3d. The new value of the force between them is

(A)-2F
(B) $F /3$
(C) $- 2 F /3$ ✓ Correct
(D) $- F /3$

Answer: (C)

Solution

The force per unit length between two parallel wires is

\frac{μ _{0} I _{1} I _{2}}{2 π d}

; call it

F

when the currents run the same way at separation

d

. Doubling one current and tripling the separation changes the magnitude to

\frac{μ _{0} ( 2 I _{1} ) I _{2}}{2 π ( 3 d )} = \frac{2}{3} F

, and reversing that current turns the attraction into a repulsion, so the force becomes

- \frac{2 F}{3}

JEE Main · 2004 · 24 Apr 2004 · Offline · Single correct option

Practise more: all JEE Main PYQs on Magnetic Effects of Current →

JEE Main · 2004 · 24 Apr 2004 · Offline · Magnetic Effects of Current

Solution

More JEE Main questions on Magnetic Effects of Current