# How can frequency be constant during refraction? [duplicate]

When entering from a rarer to a denser medium, the speed of light decreases.I know that the frequency remains constant.But if frequency is cycles/sec then doesn't that mean more speed will lead to more cycles/sec? and if the wavelength changes, should i see a different color all together? I'm not familiar with the 'complicated math' so is there another way to understand?

• possible duplicate of What determines color -- wavelength or frequency? Commented Dec 25, 2014 at 12:16
• The refraction is explained in the answer(s) to this question: physics.stackexchange.com/q/145788 Commented Dec 25, 2014 at 12:59
• The frequency has to stay constance because the phase of the ingoing wave and the outgoing wave at the boundary has to match at all times (up to a constant). If the frequencies were different, this condition would be violated. Is this what you are asking for? Commented Dec 25, 2014 at 13:13

The perception of 'colour' is loosely based on a transfer of energy from photons to photoreceptive proteins in the retina. This suggests that frequency is responsible for perception of colour since the energy of a photon is directly proportional to frequency.

The frequency does not change because the energy does not change.

This would imply that there is no change in colour with refractive index, even though the speed and wavelength of the light wave changes.

• Even though the wavelength of light in your eye is independent of the wavelength it had before. Commented Dec 25, 2014 at 12:21

Put simply the energy of a photon is given by E=hf where h is Plancks constant and f is the frequency. The photon does not transfer energy to the medium so therefore E remains constant and so must f.

• this answer of @Ed0906 cannot be right, a microwave oven works by transferring EM energy to food. If the material is absorbent then "photons" are absorbed; still, the unabsorbed part of the EM wave has the same frequency all the way through the absorption/refraction/reflection process. Commented Dec 25, 2014 at 16:01

Light consists of photons. In the period between the photon's emission and its absorption photons are indivisible units.

In every media in which the photon is not absorbed, the photon is subject to the influence of the medium. The influence is carried out mainly by the interaction between the electric field of the photon and the electrons of the medium. In vacuum, the largest distance is covered during one oscillation of the electric and the magnetic component of the photon. In a medium as well as in electromagnetic fields, these vibrations are slowed down. However, the energy content of the photon remains unchanged and any color sensor - even the human eye - stated inside the medium the same color as outside the medium.