Finding Maxwell's Equation parameters problem

[baby_1]

Homework Statement

Homework Equations

http://esclab.tw/wiki/images/math/0/a/2/0a24f9d68ba8fd1a1a8e6c6b36a00be3.png

The Attempt at a Solution

[/B]

Hello
As you see the answers of 19 and 20 problems we should try to find K or B(wave number) in wave equation.both of equations are in air space but we can't use K=(2*pi*f)/V ( F=frequency & 2*pi*f=omega , V= light velocity 3*10^8) for both of them.
could you tell me why we can't use the K=(2*pi*f)/V for both of them in air space?does it have any condition & reason that we should check them before solve the problems?

Any help appreciated

 

[Simon Bridge]

could you tell me why we can't use the K=(2*pi*f)/V for both of them

Both of what? Both problems?
Where does that relation come from?

 

[baby_1]

Thank you dear simon for you replay
My meaning is why in problem (6-19) should we use k=w/c but in problem(6-20) we should not?

Where does that relation come from?

your meaning is K=w/c?

 

[Simon Bridge]

I mean - what physical property of the wave does k represent.

The second case is in a medium - what is different about EM waves traveling in a medium compared with a vacuum?
hint: if you took k=w/c for the second case, you could not use c=3x10^8m/s.