A velocity selector consists of electric and magnetic fields described by the ex
ID: 2204627 • Letter: A
Question
A velocity selector consists of electric and magnetic fields described by the expressions E(arrowhead)= e(k) and B(arrow head)= b(j), with b = 17.0 mT. Find the value of e such that a 720-eV electron moving in the negative x direction is undeflected.
____kV/m
Explanation / Answer
energy of electron = 0.5mv^2 = 720 eV v^2 = 2*720*1.6*10^-19 (joule)/9.1*10^-31 v = 16.24*10^6 m/s vector > v = 16.24*10^6 (+i) >>>>>>> for remaining undeflected > net force is zero F-net = 0 = qE + q[v cross B] >> vector E + [v cross B] = 0 E (k) + [v (i) cross {B} (+j)] = 0 E (k) + vB [(i) cross (+j)] = 0 E (k) + vB [k] = 0 E (k) = - vB [k] comparing magnitudes E = vB = 16.24*10^6*17.0 *10^-3 (milli) E = 2.923*10^5 volt/meter hope it will work