Question

Two opposite charges are placed on a line as shown in the figure. The charge on the right is three times the magnitude of the charge on the left. Besides infinite, where else can electric field possibly be zero?

• A. between the two charges.
• B. to the right of the charge on the right.
• C. to the left of the charge on the left.
• D. the electric field is nowhere zero.

Answer 1

Answer: (C)

to the left of the charge on the left.

We know that the electric field always starts from a positive charge and ends at a negative charge. Hence field will be very strong in between the charges.

To the left of the left charge, the field due $-q$ will be towards the right and due to $3q$ will be towards the right. At some point, they will nullify each other and no field will exist.

Note that although the field starting from $3q$ will be stronger than the one ending at $-q$, on the left side of $-q$ the field due to $3q$ will become weaker due to a greater distance. At a particular point, the field due to $3q$ and opposite field due to $-q$ will become equal in magnitude and will nullify.