When light travels from air to water ,why there is change in wavelength but not frequency

firstly the speed of light in any medium is v = 1/sq.rt(mu . epsilon) which is what james clerk maxwell proved. So if both mu and epsilon change when light enters water ... the speed of light should change. This takes care of the question as to why the speed should change. Now consider a light wave, with say 10 vibrations per second. There is no reason as to why the number of vibrations in air should change when light enters water. Say if light has to lose energy, it should lose amplitude. So the number of vibration must remain constant but since speed of light in medium = frequency . wavelength ...and since speed and frequency don't change therefore wavelength changes. Yet another way of looking at it is through experiment. "The color of light is not primarily dependent on the wavelength of the light, as most people probably think. A wavelength of 389 nm is violet light in a vacuum, where the index of refraction is 1.000. However, in a medium where the index of refraction is greater than 1.000, the wavelength of violet light is not necessarily exactly 389 nm. The color mainly is dependent upon the light's frequency, which is the number of waves of the light that pass a given point in one second. If the color of light was dependent on wavelength, its color would change when it entered a medium with a different index of refraction. But it doesn't. For instance, if you look at an object in air, and then jump into a swimming pool with the object and look at it under water, the color of the object will remain the same." source: http://www.tedmontgomery.com/remarks%5C08.1-12/optics/index.html Also there is a theoretical derivation as to why this happens which depends on solving maxwells equations at the boundary with boudary conditions such that the intensity of light in air equals the sum of intensities of light which is reflected and refracted at the interface. The result of solving with such boundary conditions is that we get a change on wavelength but not frequency. I hope this suffices Cheers read less

Assuming color does not change, the wavelength and frequency cannot change thus velocity cannot change. Cute paradox! But there is a way out. We need to consider how light is transmitted through a material. What happens is the photons get absorbed by the atoms and re-emitted. Thus they start and stop the velocity between atoms is still 3*10^8 m/s. It is sort of like cars in a city. They stop at every stop light then go to the speed limit between stop lights. The average speed for the distance is less than the speed limit read less

Now, let's take a glass-air interface and pass light through it. (In SI units) In one second, ? "crest"s will pass through the interface. Now, a crest cannot be distroyed except via interference, so that many crests must exit. Remember, a crest is a zone of maximum amplitude. Since amplitude is related to energy, when there is max amplitude going in, there is max amplitude going out, though the two maxima need not have the same value. Also, we can directly say that, to conserve energy (which is dependent solely on frequency), the frequency must remain constant. read less

this is beacuse the energy remains same in both the media, and we know that E=hf, where E is the energy, h is the planck's constant and f is the frequency. therefore in case of refraction the bending of light solely depends on the wavelength and further to understand this, we know that wavelength= speed of light/frequency of light and the speed of light changes from medium to medium, thus frequency remains constant,and only wavelength changes as it is directly proportional to the speed of light. hope thi sresolved ur problem :-) read less

Light travels as waves, with the wavefronts perpendicular to the direction of motion.As light moves from air into water, it not only slows, but the wavelength changes.(Denser and rarer medium condition.). Interestingly enough, the frequency of the waves does not change as the light moves from air to water.As we know the wave's speed v is related to both the frequency f and the wavelength l : v = l/f. Combining the above expression for velocity with the definition of index of refraction, we find a relationship between the wavelength l = v/f in a medium and the wavelengthl 0 = c/f in vacuum: read less