Wave equation for a standing wave - clarification needed

In summary, the highlighted equations are both related to standing waves, but the latter one has a phase shift. This phase shift is necessary to account for the fact that the wave may not be in a tidy state at t=0 and x=0. The equations for different situations with both ends fixed, one end fixed and the other free, and both free, come from changing the phase term by ##\pi/2##. Equation 4.4.2 deals with the specific case where the amplitude is zero everywhere at t=0 and x=0 is always a node, but this is arbitrary and the wave could be at any stage at t=0 and the ruler may not start at a node.
  • #1
elemis
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Both of the highlighted equations deal with a standing wave. However, they are slightly different in the sense that the latter has a phase shift in it.

Why ?

Also, how does one go from the latter equation for a standing wave to :

2A*sinkx*sinwt. For a string with both ends fixed

And

2A*sinkx*coswt. For one end fixed and the other free

And

2A*coskx*coswt. For both free.
 
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  • #2
eq. 4.4.2 deals with the specific situation where the amplitude of the wave is zero everywhere at t=0, and the point x=0 is always a node.

However, t=0 is just when we happen to press the button on the stopwatch and x=0 is just where we happen to put the ruler at the time. These are arbitrary: the wave in front of you could be at any stage in it's motion at t=0 for eg. and the ruler may not start at a node.

The phase term is needed to account for the possibility that at t=0, and x=0, the wave is not in such a tidy state.

The other possibilities come from the phase terms ... you change from a sine to a cosine by changing phase by ##\pi/2##.
 

FAQ: Wave equation for a standing wave - clarification needed

1. What is a standing wave?

A standing wave is a type of wave that occurs when two waves with the same frequency and amplitude travel in opposite directions and interfere with each other. This creates a pattern of nodes (points of no displacement) and antinodes (points of maximum displacement) that appear stationary.

2. What is the wave equation for a standing wave?

The wave equation for a standing wave is y(x, t) = A*sin(kx)*cos(ωt), where y is the displacement of the wave, A is the amplitude, k is the wave number, x is the position, ω is the angular frequency, and t is the time.

3. How does the wave equation for a standing wave differ from the general wave equation?

The wave equation for a standing wave is a special case of the general wave equation, which describes the behavior of all types of waves. The main difference is that the general wave equation includes a term for the speed of the wave, while the wave equation for a standing wave does not, as the speed of a standing wave is zero.

4. What is the significance of the wave number in the standing wave equation?

The wave number, k, in the standing wave equation represents the number of complete cycles of the wave that occur in a unit distance. It is related to the wavelength, λ, of the standing wave by the equation k = 2π/λ. A higher wave number indicates a shorter wavelength and a more tightly packed standing wave pattern.

5. Can the wave equation for a standing wave be applied to real-world situations?

Yes, the wave equation for a standing wave can be applied to many real-world situations, such as vibrations in a guitar string or sound waves in a pipe. It is a useful tool in analyzing and understanding the behavior of standing waves in various systems. However, it is important to note that the equation is an idealized representation and may not fully capture all aspects of a real standing wave phenomenon.

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