Question

The picture above shows four pairs of uniformly charged spheres. The red spheres are positively charged; the blue spheres are negatively charged. Each sphere has the same amount of charge. Assume each pair is isolated.
For which pair is there a point between them on the dotted line where the electric field magnitude is zero and a point between them on the dotted line where the electric potential is zero?

• A. $1$
• B. $2$
• C. $3$
• D. $4$
• E. None of the pairs has points that meet these conditions

Answer 1

The correct option is E None of the pairs has points that meet these conditions

For pair 1 and 4 , the electric field will be zero at midpoint of the line joining them , because electric field is a vector quantity (the fields due to two charges will be equal and opposite to each other , so cancelled), but potential being a scalar quantity is not zero , in fact , potential of both charges will be added as both charges are same in nature .

For pair 2 and 3 , the electric field will not be zero at midpoint of the line joining them , because electric field is a vector quantity(the fields due to two charges will be equal and same in direction , so added) , now potential being a scalar quantity is zero , in fact , potential of both charges will be subtracted as both charges are opposite in nature .

So there is no pair , which satisfies the condition .