How Do You Solve the Wave Equation Using Coefficient Equations?

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SUMMARY

The discussion focuses on solving the wave equation using coefficient equations, specifically through the substitution of second differentials into the wave equation. The equation A''(x) + (w/v)^2A(x)sin(wt)=0 is derived, leading to the conclusion that A''(x) = -k^2 A(x), where k is defined as k(n) = nPI/L, with n being a quantized integer. The normal mode frequencies are expressed as w(n) = nPI/L * v. The participants seek clarification on the implications of these results, particularly regarding the relationship between wavelength and string length for part (b) of the problem.

PREREQUISITES
  • Understanding of wave equations and their derivations
  • Familiarity with second-order differential equations
  • Knowledge of harmonic motion and quantization
  • Basic concepts of boundary conditions in physics
NEXT STEPS
  • Study the derivation of the wave equation in one dimension
  • Learn about boundary conditions and their applications in wave mechanics
  • Explore the relationship between wavelength and frequency in wave phenomena
  • Investigate normal mode analysis in vibrating systems
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Students and educators in physics, particularly those focusing on wave mechanics, differential equations, and harmonic motion. This discussion is beneficial for anyone tackling problems related to wave equations and their solutions in a mathematical context.

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Homework Statement



[PLAIN]http://img33.imageshack.us/img33/8236/waveeq.jpg



The Attempt at a Solution



We calculate second differential with respect to x, and t, substitute into the wave equation.

We then equate the coefficients: [A''(x) + (w/v)^2A(x)]sin(wt)=0

We know from SHM equation that: A''(x) = -(w/v)^2A(x), and hence A''(x) = -k^2 A(x)

But where do we go from here? Any hints?

Also, what about part b?
 
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From A''(x) = -k^2 A(x), we seek a solution of the form A(x) = Csin(kx + psi)

Apply our boundary conditions of y(0,t) and y(L,t) both = 0.

We end up with sin(kL) = 0, where kL varies from 0 to 2PI, this implies that kL=nPI where n=1,2,3...

Because it's quantised, we can say k(n) = nPI/L, where n=1,2,3...

Since k = w/v, w(n) =nPI/L . vWhere w(n) are the normal mode frequencies.

Could someone verify this is correct?
 
Also, any clues for b)?
 
Looks good for part (a).
For (b), I'm not quite sure what they are getting at. In a sense, you already showed this in your derivation for part (a). Maybe they want you to think in terms of the wavelength λ and how it relates to the string length L.
 

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