Question

A system consists of a thin charged wire ring of radius r and a very long uniformly charged wire oriented along the axis of the ring, with one of its ends coinciding with the center of the ring. The total charge on the ring is q, and the linear charge density on the straight wire is $\lambda$. The interaction force between the ring and the wire is :

• A. $\frac{\lambda q}{4\pi {\epsilon }_{0}r}$
• B. $\frac{\lambda q}{2\sqrt{2}\pi {\epsilon }_{0}r}$
• C. $\frac{2\sqrt{2}\lambda q}{\pi {\epsilon }_{0}r}$
• D. $\frac{4\lambda q}{\pi {\epsilon }_{0}r}$

Answer 1

The correct option is A $\frac{\lambda q}{4\pi {\epsilon }_{0}r}$

Net force $F_{net}=q{E}_x$

Electric field due to a long straight wire of charge density $\lambda$ at one of its end is given by, $E=\frac{\lambda }{4\pi {\epsilon }_{0}r}$

$F=q\frac{\lambda }{4\pi {\epsilon }_0}=\frac{\lambda q}{4\pi {\epsilon }_{0}r}$