Question

Three charges $-2q,q,q$ are placed on the vertices of an equilateral triangle. At the incentre of the triangle,

• A. the field is zero but the potential is non-zero.
• B. the field is non-zero but the potential is zero.
• C. both the field and the potential is zero.
• D. both the field and the potential is non-zero.

Answer 1

Answer: (B)

The field will start from the two $q$ charges and end at the $-2q$ charge. Hence, field will not be zero. In fact, the negative charge increases the field strength.

Since it is an equilateral triangle, the incenter is equidistant from all the three charges. The potential due to a number of charges is just the arithmetic sum of the individual potentials.

Since there are two positive $q$ charges and one negative charge $-2q$, the potential is zero.