CBSE Class 12-science Answered

In (a), the field (E) is upward, so the negatively charged electron (e) experiences a downward force F = Ee.

Force experienced by electron of mass m and charge e is:

The acceleration of the electron is

Now, equations of motion

As the body is starting from rest, u = 0

The time required by the electron to fall through a distance h is given as:

In (b), the field (E) is downward, so the positively charged electron (e) experiences a downward force F = Ee.

Force experienced by proton of mass m_p and charge e is:

The time required by the proton to fall through a distance h is given as:

Thus, the heavier particle (proton) takes a greater time to fall through the same distance.

In the case of free fall under gravity, the time of fall is independent of the mass of body.

The acceleration of electron and proton are > acceleration due to gravity. Thus, the effect of acceleration due to gravity is ignored in this case.