Single Choice

Two long straight parallel wires, carrying (adjustable) current $$I_1$$ and $$I_2$$, are kept at a distance d apart. If the force 'F' between the two wires is taken as 'positive' when the wires repel each other and 'negative' when the wires attract each other, the graph showing the dependence of 'F', on the product $$I_1I_2$$, would be

A
B
C
D
Correct Answer

Solution

The force between two wires per unit length is: $$F=\dfrac{\mu _0}{2 \pi d} I_1I_2$$

When,$$I_1$$ and $$I_2$$ are in in the same direction, the wires attract each other, and $$F \lt 0$$
When,$$I_1$$ and $$I_2$$ are in opposite direction, the wires repel each other, and $$F \gt 0$$
The plot is a straight line since $$F \propto I_1I_2$$
The slop is negative since sign of force is opposite to the product $$I_1I_2$$( same direction product is positive, opposite direction product is negative.

SIMILAR QUESTIONS

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A straight, long wire carries a current of $$20\ A$$. Another wire carrying equal current is placed parallel to it. If the force acting on a length of $$10\ cm$$ of the second wire is $$2.0\times 10^{-5}N$$, what is the separation between them?

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Two parallel wires separated by a distance of $$10\ cm$$ carry currents of $$10\ A$$ and $$40\ A$$ along the same direction. Where should a third current be placed so that it experiences no magnetic force ?

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The wires which connect the battery of an automobile to its starting motor carry a current of 300 A (for a short time). What is the force per unit length between the wires if they are 70 cm long and 1.5 cm apart? Is the force attractive or repulsive?

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