# 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?