In the figure, an a-particle moves a distance $l$ in a uniform electric field $\vec E$ as shown. Does the Electric Field do a positive or a negative work on the a-particle? Does the electric potential energy of the a-particle increase or decrease?
Answer & explanation
Correct answer: option 1
The correct answer is Option (4) → Positive, increases
$\vec{E}$ is to the right, displacement of $\alpha$ is to the left
$\text{Force on } \alpha\ (q>0) \text{ is along } \vec{E}$
$\text{Force opposite to displacement}$
$W = \vec{F}\cdot \vec{s} < 0$
$\text{Work done by electric field is negative}$
$\Delta U = -W > 0$
$\text{Potential energy increases}$
Work is negative and potential energy increases.