The charges $2 \mathrm{q},-\mathrm{q},-\mathrm{q}$ are located at the vertices of an equilateral triangle. At the circumference of the triangle

• A

  the field is zero but potential is not zero.
• Correct answer
  B

  the field is non-zero but the potential is zero.
• C

  both, field and potential are zero.
• D

  both, field and potential are non-zero.

Solution

From charge configuration, at the centre electric field is non-zero.
Potential at the centre due to $2 \mathrm{q}$ charge $\mathrm{V}_{2 \mathrm{q}}=\frac{2 \mathrm{q}}{\mathrm{r}}$ and potential due to $-\mathrm{q}$ charge $\mathrm{V}_{-\mathrm{q}}=-\frac{\mathrm{q}}{\mathrm{r}} \quad(\mathrm{r}=$ distance of centre point $)$ $\therefore \quad$ total potential $\mathrm{V}=\mathrm{V}_{2 \mathrm{q}}+\mathrm{V}_{-\mathrm{q}}+\mathrm{V}_{-\mathrm{q}}=0$

Hence, the correct answer is option: 'B'.