Question

No of null points in a square

• A. 1
• B. 3
• C. 0
• D. More than 3

Answer 1

Answer: (A), (B)

1, 3

Answer 2

The number of null points (locations where the net electric field is zero) in a square configuration of charges depends on the arrangement of the charges.

1. Identical Charges: If all four charges at the corners of the square are identical (e.g., all $+q$ or all $-q$), there is exactly one null point at the center of the square due to symmetry.

2. Alternating Charges: If charges are arranged alternately ($+q, -q, +q, -q$) at the corners, the center of the square is also a null point. It can be shown that in this configuration, there is only one null point at the center.

3. Specific Opposite Charges: Consider charges $+q$ at two opposite corners and $-q$ at the other two opposite corners (e.g., $+q$ at (0,a) and (a,0), and $-q$ at (0,0) and (a,a)). In this case, the center is a null point, and there are two additional null points located symmetrically outside the square. Thus, there are a total of three null points.

Therefore, depending on the charge distribution, the number of null points can be 1 or 3 for common symmetric configurations.