Question

Two point charges $a$ and $b$ whose magnitudes are same are positioned at a certain distance from each other. $a$ is at origin. Graph is drawn between electric field strength and distance $x$ from $a.E$ is taken positive if it is along the line joining from $a$ to $b$. From the graph it can be decided that

• A. $a$ is positive, $b$ is negative
• B. $a$ & $b$ both are positive
• C. $a$ & $b$ both are negative
• D. $a$ is negative, $b$ is positive

Answer 1

The correct option is A $a$ is positive, $b$ is negative

From graph it can be observed that field is always in the +ve direction. This means a must be +ve and b must be -ve.
If both are positive, then field must become zero and change it's direction afterward.
If both are negative, then field must be in -ve direction when it is close to a.
a -ve and b +ve means field must always be -ve.