Need the correct time dependent function

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SUMMARY

The discussion focuses on deriving the time-dependent function for the motion of a free electron in an electric field, governed by the equation m((d^2)x)/(dt^2) = -eE. The solution involves recognizing that both position x and electric field E exhibit time dependence in the form of exp(iwt), leading to the conclusion that the second derivative of x must equal -(w^2)x. The correct time-dependent function is confirmed to be x = x0 * exp(iwt), where x0 is a constant amplitude, demonstrating the relationship between the motion of the electron and the oscillating electric field.

PREREQUISITES
  • Understanding of classical mechanics, specifically Newton's second law.
  • Familiarity with complex exponentials and their applications in physics.
  • Knowledge of electromagnetic theory, particularly wave equations.
  • Basic calculus, including differentiation and second derivatives.
NEXT STEPS
  • Study the derivation of the wave equation in electromagnetic theory.
  • Learn about the application of complex numbers in physics, particularly in wave mechanics.
  • Explore the implications of the second derivative in motion equations.
  • Investigate the relationship between electric fields and particle motion in quantum mechanics.
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Students of physics, particularly those studying electromagnetism and wave mechanics, as well as educators looking for clear examples of time-dependent functions in classical mechanics.

_Andreas
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Homework Statement



The equation of motion of a free electron in an electric field is

m((d^2)x)/(dt^2) = -eE (Eq. 1)

If x and E have the time dependence exp(iwt), where w=angular frequency, then

-(w^2)mx = -eE (Eq. 2)

What does the time dependent function whose second derivative equals -(w^2)x look like?

The Attempt at a Solution



I know from my papers that the electromagnetic wave is given by

E=E0exp(iwt),

and I guess the equation I'm after looks similar. The second derivative of x*exp(iwt) would give me the correct answer, but x=x0*exp(iwt) doesn't seem to do, because equation 2 says x and not x0.
 
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x=x0exp(iwt)

d2x/dt2=-w^2 x0 exp(iwt) = -w^2 x
 
christianjb said:
x=x0exp(iwt)

d2x/dt2=-w^2 x0 exp(iwt) = -w^2 x

Ah, I forgot that the factor exp(iwt) will still be there after the derivation :rolleyes:

Thanks!
 
Last edited:

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