Now imagine that a beam of moving electrons enters the quadrupole, with velocity parallel to the charged rods. When the beam enters the device, its cross-sectional profile is circular. What will the beam look like when it exits the quadrupole on the other side

The beam of electrons would be flattened into a oval that is long in the x-axis and short in the y-axis.

Explanation:

A beam of moving electrons enters the quadrupole, with velocity parallel to the charged rods. When the beam enters the device, its cross-sectional profile is circular. On the other side, the beam of electrons would be flattened into a oval that is long in the x-axis and short in the y-axis.

The directions is shown in figure.

another example of kinetic energy would be,

kinetic energy   >     moving energy

answer   >   letter choice (c),   a hammer falling off a table.

hope that !                                         : )