# A question on wave nature of EM radiation

1. Jul 11, 2008

### SpaceExplorer

There is a EM radiation of frequency suppose x Hz.Let it has to travel a distance of y m.Now what's the time required for the radiation to travel the distance?The question seems to be very easy, but my confusion is in how can the frequency,distance,speed and time can be related? Can someone give the relation along with the answer?

2. Jul 11, 2008

### peter0302

v == c
s = ct
f = c / wavelength

Wavelength and frequency have nothing to do with the distance the light travels or the time it takes to get there. The frequency describes the oscillation of the electromagnetic field over time. The "wavelength" of the light is not the physical size of the photon but the distance the photon travels in going through one complete EM cycle.

Imagine a little blob of light moving in a straight line quickly oscillating from red to black to blue to black to red and so forth as it moves. The red and the blue represent the oscillations of the EM field. The wavelength is the distance the blob travels while doing a complete red/blue cycle.

3. Jul 12, 2008

### zozoconde

hi
electromagnetic radiation speed is c i.e speed of light which is 3.0 x 10 ^8 m/s in air
It does not change except if it is travelling in a different medium
So divide distance y by c , you get the time t

Last edited: Jul 12, 2008
4. Jul 12, 2008

### Andy Resnick

As others have written, there's a clean relationship between the frequency, wavelength and speed (c = $$\lambda\nu$$). Confusion usually comes in when trying to understand this in terms of quantum mechanics, specifically the photon picture and the idea of refeactive index.

For your question, since you did not give a medium, the answer can't be given. But the general answer is t= c/n *y. Again, sources of confusion exist here, in terms of phase vs. group velocity. But, since you are assuming monochromatic light, there shouldn't be any issues.