Question

A proton is kept at rest. A positively charged particle is released from rest at a distance $d$ in its field. Consider two experiments; one in which the charged particle is a proton and in another a positron. In the same time $t$, the work done on the two moving charged particles is

• A. same as the same force law is involved in the two experiments
• B. less for the case of a positron, as the positron moves away more rapidly and the force on it weakens
• C. more for the case of a positron, as the positron moves away a larger distance
• D. same as the work done by charged particle on the stationary proton

Answer 1

Answer: (C)

Force between two protons $=$ force between a proton and a positron. As positron is much lighter than proton, it moves away a larger distance compared to proton. As work done $=$ force $\times$ distance, therefore in the same time $t$, work done in case of positron is more than that in case of proton.