A velocity selector for ions uses perpendicular electric and magnetic fields. If the electric field used were 800 V/m, what magnetic field would allow the selection of a velocity of 4000 m/s?
A) 0.0400 T
B) 0.0800 T
C) 0.160 T
D) 0.200 T
E) 0.500 T

Question

Quizplus · Accepted Answer

The velocity selector works by applying perpendicular electric and magnetic fields that are adjusted to select a specific velocity of ions passing through it. The magnetic field must be adjusted to balance the force on the ions due to the electric field, so that only ions with the desired velocity are allowed to pass through.

The formula for the velocity selector is:

v = E/B

where v is the velocity of ions, E is the electric field strength, and B is the magnetic field strength.

We are given that the electric field strength is 800 V/m and the desired velocity of ions is 4000 m/s. Therefore, we can rearrange the formula above to solve for the magnetic field strength:

B = E/v

B = (800 V/m)/(4000 m/s)

B = 0.2 T

Therefore, the magnetic field strength needed to select ions with a velocity of 4000 m/s is 0.2 T. The nearest value to this is 0.200 T, which is choice D.

A Velocity Selector for Ions Uses Perpendicular Electric and Magnetic