Question

Two equal and positive charges are placed at $a$ and $-a$ on $x$-axis, then graph of electric field along $x$-axis with distance $x$ will be

• A.
• B.
• C.
• D.

Answer 1

The correct option is B

As we know that,
$E=\frac{kQ}{R^2}$, where $R$ is the distance from charge.
Here, electric field at any point between the charges is:
$E=\frac{kQ}{r^2}-\frac{kQ}{(2a-r{)}^2}$
where $r$ is the distance of point from one of the charges.

Now, beyond the point $a$ and $-a$, the field will be:
$E=\frac{kQ}{x^2}+\frac{kQ}{(2a+x{)}^2}$
where $x$ is the distance from the nearest charges.
Plotting these equations we get graph b.