Question

In figure below, the point charge $Q_{1}$ causes an electric potential of $60 \,V$ and an electric field strength of $30 \,V m ^{-1}$ at $P$ and the point charge $Q_{2}$ separately causes a potential of $120\, V$ and a field strength of $40\, V m ^{-1}$ 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 $180\, V$.
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 $50\, V\, m ^{-1}$ as shown.