Calculating Electron Velocity in Crossed E and B Fields

[Schaus]

Homework Statement

What velocity does an electron need to have in order to travel straight through the crossed E and B fields, given that E = 1.0 x 105 N/C and B = 0.40 T?
Answer: 2.5 x 10⁵ m/s

Homework Equations

E=F/Q
F=BIl
F=QvB[/B]

The Attempt at a Solution

1.0 x 10⁵N/C / 1.6 x 10^-19 = 6.25 x 10²³N. I rearranged F=QvB - v=F/QB
v = 6.25 x 10²³N/ (1.6 x 10^-19)(0.40T). I'm left with 9.765 x 10⁴² but I know this isn't my velocity but I'm confused on where to go or what I did wrong.

 

[Wadih Hanache]

They give you the electric field, not force.
F=QE

 

[Schaus]

I'm still at a loss then. I've switched to the E=KQ/r² formula and rearranged it to get radius but I don't know how that helps me find velocity.

 

[Schaus]

I found the answer but I'm not sure exactly what I did. I found a formula for electromagnetism on wikipedia - F=(v x B) and I took 1.0 x 10⁵/0.40T and got my answer.

 

[Wadih Hanache]

You were on the right path with F=QvB, and since (E) is given, I used the formula F=E*Q to replace (F) in the first equation.

Then got EQ=QvB
v=EQ/QB
v=E/B and got the answer 2.5*10^5 m/s.
which is the same answer you just found as well.

Sorry for any confusion, hopefully this helped.

 

[Schaus]

Awesome! Thank you! This makes much more sense!