Question

Two charges $Q$ coulomb and $-Q$ coulomb are placed on a straight line as shown in the figure. Choose the correct graphical representation of potential $\left(V\right)$ versus distance $\left(r\right)$.

• A.
• B.
• C.
• D.

Answer 1

The correct option is C


In region $\text{I}$:
distance from $+Q$ is less than the $-Q$.

As, potential at a distance due to point charge is inversely proportional to the distance.

We can say that, potential due to $+Q$ will be greater than the potential due to $-Q$ in the region $\text{I}$

$V_{+Q}>V_{-Q}$

Therefore, the net potential must be positive,i.e.,

$V_{net}=+ve$

In region $\text{II}:$
From, $\text{P}\to \text{Q}\to V_{+Q}>V_{-Q}\Rightarrow V_{net}=+ve$

From, $Q\to R\to V_{-Q}>V_{+Q}\Rightarrow V_{net}=-ve$

In region $\text{III}:$
Potential due to $+Q$ will be less than the potential due to $-Q$ as distance from $+Q$ charge is more than $-Q$ charge.

$V_{+Q}<V_{-Q}$

Therefore, the net potential must be negative,i.e.,

$V_{net}=-ve$


Hence, option (c) is the only correct alternative.