Question

A thin bar magnet of length 2 L is bent at the mid-point so that the angle between them is 60${}^o$. The new length of the magnet is

• A. $\frac{L}{2\sqrt{3}}$
• B. $\frac{\sqrt{3}L}{2}$
• C. $L$
• D. $\frac{2L}{3}$

Answer 1

The correct option is C $L$

When a thin bar magnet of length $2L$ is bent at mid-point as mentioned , it will have two sides , each of length $L$ , inclined to an angle of ${60}^o$ with each other . The two poles will be at the end points of magnet of length $2L$ . Now , the new length of magnet will be the shortest distance between south and north poles .

By joining the two ends of magnet of length $2L$ , we get a third side . These , three sides will form an equilateral triangle of side (by geometry) $L$ . Now , the shortest distance between two poles is $L$ , which is the new length of magnet .