(adsbygoogle = window.adsbygoogle || []).push({}); a velocity selector consists of magnetic and electric fields. if B= 0.015 find the value of E such that a 750 eV electron is moving along the + x- axis and is undeflected.

this is what i did..

the magnetic force=electric force so qvB=qE or vB=E

K= .5 mv^2 and r= mv/qB so k =[.5r^2q^2B^2]/m and if you simplify you get:

r= [(2km)^.5]/qB

r= {[2*750*1.6*E-19*9.11E-31]^.5}/1.6E-19*.015= 1.38E-16

if v=rqm/m then v = [1.38E-6*1.6E-19*.015]/9.11E-31 = 3.64E3

since E= vB then E= 3.64E3*0.15= 5.45E1

but this is not the answer

the answer is 244 KV/m

someone please help its driving me mad and i have a test soon

thanks!

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# Homework Help: I dont understand where i went wrongplease help

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