Understanding Light: Frequency vs Wavelength in Different Mediums

In summary, when light goes from one medium to another, its velocity changes, causing a change in either the frequency or wavelength (or both). The frequency remains constant while the wavelength changes, as explained by the equation \lambda = n\lambda', where n is the index of refraction and \lambda' is the wavelength in the medium. This is supported by the concept of continuity in wave functions and can be mathematically derived using the refractive index formula, n = c/v = f\lambda/v = \lambda/\lambda'.
  • #1
informtohagrid
7
0
Hi..when light goes from one medium to other medium (like air to glass or glass to air) its velocity changes(either increases or decreases)..if velocity is changing then frequency or wavelength should also be changing..i want to know which one changes..frequency or wavelength or both...
I think frequency changes..is this correct..
 
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  • #2
nope, wavelength. *shrug*... I guess I could explain in more detail. Say cars enter a tunnel at a frequency of one per second. At some point, assume the traffic speed decreases (perhaps there is a highly visible radar trap): there must still be one car per second passing that point, otherwise the cars would keep piling up (until no more could fit into the tunnel), so the *length* between cars must decrease there..
 
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  • #3
No, the frequency f and hence the energy hf remain unchanged. The wavelength change is simply

[tex]\lambda[/tex] = n[tex]\lambda[/tex]'

where
n is the index of refraction
[tex]\lambda[/tex]' is the wavelength in the medium
 
  • #4
are there any theoritical or experimental proof that only wavelength changes when light goes from one medium to other medium?
 
  • #5
I agree with the wavelength changing, however I would not bet my life on it.
 
  • #6
The frequency has to be the same on both sides of the boundary between two media because the wave function has to be continuous at all times, that is, it can't "jump" discontinuously as it crosses the boundary.

For a classical analogue, consider a wave traveling down a stretched string which is fastened to a thick rope at one end. The speeds of the wave are different along the string and the rope. The string just before the junction has to oscillate at the same frequency as the rope just after the junction, in order for the string and the rope to stay connected at the junction.
 
  • #7
Helios said:
No, the frequency f and hence the energy hf remain unchanged. The wavelength change is simply

[tex]\lambda[/tex] = n[tex]\lambda[/tex]'

where
n is the index of refraction
[tex]\lambda[/tex]' is the wavelength in the medium


Any mathematical or theoritical derivation you have for the relation above...
 
  • #8
Let v be the velocity of light in the medium

n = [tex]\frac{c}{v}[/tex] = [tex]\frac{f\lambda}{v}[/tex] = [tex]\frac{\lambda}{\lambda'}[/tex]
 
  • #9
Strictly, Helios, you should have a ratio of two refractive indices there.
 

FAQ: Understanding Light: Frequency vs Wavelength in Different Mediums

1. What is the difference between frequency and wavelength?

Frequency refers to the number of wave cycles that pass through a given point in one second, while wavelength is the distance between two consecutive peaks of a wave. In simpler terms, frequency is the measure of how often a wave occurs, while wavelength is the measure of the length of each wave.

2. How does light behave differently in different mediums?

Light travels at different speeds in different mediums due to differences in their density and composition. This causes light to bend or refract when it enters a new medium, which can affect the frequency and wavelength of the light. For example, light travels slower in water than in air, causing it to bend and appear distorted when viewed from above the water's surface.

3. How does the frequency and wavelength of light affect its color?

The frequency and wavelength of light determine its color. Light with a higher frequency and shorter wavelength appears bluer, while light with a lower frequency and longer wavelength appears redder. This is because our eyes perceive different wavelengths as different colors.

4. Can light travel through all mediums?

No, light cannot travel through all mediums. For example, light cannot pass through opaque objects like walls because the particles in the object absorb or reflect the light, preventing it from passing through. However, light can travel through some translucent mediums, like glass, which allows some light to pass through while scattering or reflecting the rest.

5. How does the concept of frequency and wavelength apply to other forms of electromagnetic radiation?

The concept of frequency and wavelength applies to all forms of electromagnetic radiation, including radio waves, microwaves, infrared, ultraviolet, x-rays, and gamma rays. Each type of radiation has a unique frequency and wavelength, which determines its properties and interactions with matter.

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