# Homework Help: Magnetic force

1. Apr 19, 2006

### spoonthrower

In a television set, electrons are accelerated from rest through a potential difference of 19 kV. The electrons then pass through a 0.29 T magnetic field that deflects them to the appropriate spot on the screen. Find the magnitude of the maximum magnetic force that an electron can experience.

Here are my thoughts so far.... this is all i know....
B=F/(qv)
B=.29
19kV=19000 V
I need to find the velocity of the electron to solve for F, the only problem is.....

2. Apr 19, 2006

### neutrino

Electrons gain energy when the are accelerated. Once they escape the influence which was accelarates them, the energy is purely kinetic.

3. Apr 19, 2006

### spoonthrower

i dont understand still....do i have to use the kinetic energy theorom??? and if i do what do i plug into it??? thanks

4. Apr 19, 2006

### EbolaPox

We know that the maximum magnetic force occurs when velocity is maximum.

The electron is being accelerated through a potential difference. By the Work-Energy Theorem

$$1/2 mv^2 = qV$$
When all the energy the electron gains from the potential difference goes to kinetic energy, its velocity is maximized.

Solve for velocity. Does that help?