physics
posted by Anonymous .
What magnetic field is required to constrain an electron with a kinetic energy of 400eV to a circular path of radius .80m? (answer: 8.4x10^5T) What equation(s) do I use? Any help is appreciated!

V = sqrt (2E/m) relates velocity to energy.
E = 400 eV *1.6*1019 J/eV = 6.4*10^17 J
e V B = m V^2/R
That equates the magnetic force to the centripetal force
B = m V/(R e) = [sqrt(2 E m)]/(R e)
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