- #1

popo902

- 60

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## Homework Statement

an electron accelerated from rest through potential difference V1=0.868 kV enters the gap between two parallel plates having separation d = 21.9 mm and potential difference V2= 91.2 V. The lower plate is at the lower potential. Neglect fringing and assume that the electron's velocity vector is perpendicular to the electric field vector between the plates. In unit-vector notation, what uniform magnetic field allows the electron to travel in a straight line in the gap?

## Homework Equations

KE = QV

KE = 1/2 mv^2

E= -V/d

E=vB

FE = QE

FB = Qv X B

## The Attempt at a Solution

i know that Q and m are the charge an mass of an electron

to calculate E, i used V2, 91.2V.

I use the equations to solve for v

i know that for the electron to go straight through, the FE=FB,

so i got E = vB

then i solved for B

and since B is a cross product of vectors on an xy plane, It HAS to only have a direction perpendicular to them on the z axis

it asks for the answer in vector notation so

in the end, i get 0i + 0j + 2.38e-4k T

but it's wrong...

I have a feeling that this is supposed to be one of the easier questions too :S