Question

Two large sized charged plates have a charge density of + σ and -σ. The resultant force on the proton located midway between them will be:

• A. $\sigma e / \epsilon_0$
• B. $\sigma e / 2\epsilon_0$
• C. $2\sigma e / \epsilon_0$
• D. zero

Answer 1

Answer: (A)

$\sigma e / \epsilon_0$

Answer 2

Each plate produces an electric field of $\frac{\sigma}{2\epsilon_0}$. In the region between the plates, these fields add up to $\frac{\sigma}{\epsilon_0}$. The proton experiences a force $e\frac{\sigma}{\epsilon_0}$.