# Speed of electron into electric/magnetic fields

## The Attempt at a Solution

attached is my attempt to answer part b) of this question. I have been told its wrong but don't know what i'm missing, any ideas?

#### Attachments

• physics 30.jpg
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sorry the image didn't show up like planned i'll type it out.

b) Calculate the speed of the electron moving into the electric and magnetic fields....

we have a diagram in part a) that shows an electron moving into the plane of the page.

were given:
V = 2000 V between charged plates
d= 0.080 m between charged plates
B = 0.0028 T

The electron enters the electric field, which is perpendicular to the magnetic field, and passes through both fields undeflected.

Here now is my attempt at an answer.

V=2000 V
d= 0.080 m
B = 0.0028 T
q = 1.60 x 10^-19 C

E = F/d E = 2000 V / 0.080 m = 25000 V/m

F= Bqvelocity

F= Eq
(25000V/m)(1.60 x 10^-19)
= 4 x 10^-15 N

hage567
Homework Helper
I can't see the image yet, so correct me if I'm wrong about what's going on.

What have you done with the magnetic field in your calculation? If the electron passes undeflected, that means the force from the electric field and the force from the magnetic field must cancel out. So at what speed does that happen? I think you have started out OK, you just need to finish. Why is your work considered wrong?