I Wave Equation

1. May 17, 2017

Pushoam

In the wave equation$\frac {\partial^2 \psi} {\partial x^2}=\frac{1}{v^2}\frac{\partial^2 \psi}{\partial t^2}\tag{1}$, v is the speed of the wave propagation.
With respect to which reference frame is this speed measured( in general)?

2. May 17, 2017

Staff: Mentor

What is the context of your question, classical physics, relativity or quantum mechanics?

3. May 17, 2017

Pushoam

classical physics and relativity

4. May 17, 2017

Staff: Mentor

What do you think v represents for each one then?

5. May 17, 2017

Pushoam

v represents speed of the wave propagation.
For example, if we take wave on a string, then the speed is measured from the lab frame.
But how do we know that the speed should be measured from the lab frame( just by knowing the wave equation)?
And why can't we decide the reference frame in case of electromagnetic waves?