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 also a proton and in another, a positron. In the same time t, the work done on the two moving charged particles is ______.

Options

• same as the same force law is involved in the two experiments.

• less for the case of a positron, as the positron moves away more rapidly and the force on it weakens.

• more for the case of a positron, as the positron moves away a larger distance.

• same as the work done by charged particle on the stationary proton.

Answer 1

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 also a proton and in another, a positron. In the same time t, the work done on the two moving charged particles is more for the case of a positron, as the positron moves away a larger distance.

Explanation:

The force between two protons is equal to the force between proton and a positron because their charges are the same. As the mass of positron is much lesser than the proton, (1/1840 times) it moves away through a much larger distance compared to the proton.

Change in their momentum will be the same. So, the velocity of a lighter particle will be greater than that of a heavier particle. So, the positron is moved through a larger distance.

As work done = force x distance. As forces are the same in case of proton and positron but distance moved by positron is larger, hence, work done will be more.