Physics Van 3-site Navigational Menu

Physics Van Navigational Menu

Q & A: electromagnetic waves

Learn more physics!

Most recent answer: 10/22/2007
Q:
I am very confused about the topic electromagnetic waves. Can u please answer my questions?

1)Are all the rays in an electromagnetic specturm transverse waves?

2)Do all the rays in an electromagnetic wave have the same speed of 3*10^8 ms^-1?

3)Does the wavelength affect the period (the time taken to produce one complete wave) of a wave?

4)Does the wavelength affect the frequency of the wave?

5)Why does the wavelength change when the wave enters from one medium to another?

6)Why is the fomula to find the speed of a wave v=wavelength/period?

*Please use simpler words as I am not good in physics. Thanks a lot =)
- Anonymous
A:
1. yes
2. yes, in vacuum
3. yes, wavelength = period x speed
4. yes, frequency = speed/wavelength
5. Aha, tougher question. The speed is different in different media. Since the frequency  doesnít change, the wavelength must change proportional to the speed.

Why doesnít the frequency change? The wave in the new medium is driven by the fields from the old medium, and they wiggle back and forth with some frequency. So they drive wiggles at that same frequency.

Why does the speed change? That was first understood by Lorentz. The wave drives charged particles into oscillation at its frequency. They re-radiate more waves. Itís tricky, but the sum of the old wave and the new one lags behind where the old wave would have been, in effect moving more slowly.

Mike W.



(published on 10/22/2007)

Follow-up on this answer.