Assuming a classical picture of the atom, an electron is captured into a circular orbit about a spherically shaped, singly charged ion, thus neutralizing it. In the frame of reference of the ion, the neutral atom acquires a component of velocity that is
A)in the opposite direction to that of the incoming electron.
B)equal to zero.
C)in the same direction as that of the incoming electron.
D)unpredictable because insufficient information has been given.

Question

Quizplus · Accepted Answer

In the frame of reference of the ion, when an electron is captured into orbit around it, the system's center of mass must remain stationary if no external forces are acting on it. Since the electron has momentum in a certain direction at the moment of capture, to conserve momentum, the newly formed neutral atom (ion + electron) must have a component of velocity in the same direction as the incoming electron. This ensures the total momentum of the system before and after the capture remains constant.

Assuming a Classical Picture of the Atom, an Electron Is