Question

Two charges $q_1$ and $q_2$ are kept on $x-$ axis and electric field at different points on $x-$ axis is plotted against $x$. Choose correct statement about nature and magnitude of $q_1$ and $q_2$.

• A. $q_1-ve,q_2+ve;\left|q_1\right|<\left|q_2\right|$
• B. $q_1-ve,q_2+ve;\left|q_1\right|>\left|q_2\right|$
• C. $q_1+ve,q_2-ve;\left|q_1\right|>\left|q_2\right|$
• D. $q_1+ve,q_2-ve;\left|q_1\right|<\left|q_2\right|$

Answer 1

The correct option is B $q_1-ve,q_2+ve;\left|q_1\right|>\left|q_2\right|$


We can see from the graph that:

$\left(1\right).$
Just to the left of $q_1$, the electric field is $+\alpha$ (let) or toward right (toward $q_1$).
Hence, $q_1$ is negative because $x$ is negative and $E$ is positive.

$\left(2\right).$
Just to the right of $q_2$, the electric field is $+\alpha$ (let) or toward right (away from $q_2$).
Hence, $q_2$ is positive because $x$ is positive and $E$ is positive.

$\left(3\right).$
$E_{\text{net}}=0$ near $q_2$.
Hence, $\left|q_1\right|>\left|q_2\right|$ because $E\propto \frac{q}{r^2}$