Question

In figure below, the point charge $Q_1$ causes an electric potential of $60V$ and an electric field strength of $30V{m}^{-1}$ at $P$ and the point charge $Q_2$ separately causes a potential of $120V$ and a field strength of $40V{m}^{-1}$ at $P$.

Which one of the following gives possible value of potential and filed strength at $P$ due to the joint action of $Q_1$ and $Q_2$ ?

	Potential(V)	Field(V $m^{-1}$ )
a	180	70
b	180	50
c	135	50
d	60	10

• A. a
• B. b
• C. c
• D. d

Answer 1

Answer: (B)

The electric potential at $P$ due to charges $Q_1$ and $Q_2$ is the algebraic sum of the potentials due to individual charges at point $P.$ Hence, the electric potential at is now $(120+60)$ or $180V$.
On the other hand, the electric field strength at $P$ is the resultant of fields due to charges $Q_1$ and $Q_2$. The value of the resultant field strength is $50V{m}^{-1}$ as shown.