Electric and magnetic field

[dougouk]

Homework Statement

Electrons are accelerated from rest in a CRT. These electrons now pass through a magnetic field of 1.50  10-2 T that is perpendicular to an electric field of 3.25  105 N/C. The electrons are not deflected. Assuming the electrons are traveling perpendicular to these fields, what is the potential difference across the CRT?
a. 1.34  103 V
b. 6.47  10-5 V
c. 1.31  10-19 V
d. 6.06  10-27 V

Homework Equations

Fm = qvB
Fe =qE
E = V/d

The Attempt at a Solution

I got stuck just trying to get the formula right...
How do i separate for V when I don't have d?

 

[zorro]

Hint: Since the electrons are not deflected, the net force on the electrons is 0.
You can find out their velocity using my hint.
Then find out their kinetic energy.
Use the formula K.E. = eV where V is the potential difference and e is the charge of an electron.

P.S. - This is not mathematics :|

 

[Dadface]

Hello dougo,
You were trying to calculate V,the voltage across the plates which sets up the electric field and the question does not give enough information for you to be able to do that.The question as you presented it is ambiguous but I think you will find the voltage wanted is the accelerating voltage in the electron gun.If the electrons are accelerated from rest by a voltage V then the KE they acquire is equal to eV.From this you can calculate v,the speed of thre electrons and then use the top two equations you wrote above.You may find it useful to google "velocity selector".

 

[dougouk]

Thx guys~