question_answer

4 point charges each +q is placed on the circumference of a circle of diameter 2d in, such a way that they form a square. The potential at the centre is

A)  0                                            

B)  \[\frac{4q}{d}\]

C)  \[\frac{4d}{q}\]                                               

D)  \[\frac{q}{4d}\]

Correct Answer: B

Solution :

                 Potential at centre due to all charges are \[=\frac{1}{4\pi {{\varepsilon }_{0}}}\left[ \frac{q}{d}+\frac{q}{d}+\frac{q}{d}+\frac{q}{d} \right]\] \[=\frac{1}{4\pi {{\varepsilon }_{0}}}\frac{4q}{d}\]in SI units \[=\frac{4q}{d}\]in CGS units