# Does snell's law apply ?

1. Nov 24, 2012

### Jimmy Chung

Does Snell's law apply in refraction when the light ray is along the normal line? Utilizing snell's law, the index of refraction (n) would be zero.

nr= ni(sin θi)/sinθr

Sin(θi)= 0 therefore, nr=0

However,utilizing the formula for index of refraction (n=c/v), the index of refraction would not be zero as both v and c are positive.

Are light rays along the normal line and not bending refraction at all? If so, which calculation of the index of reflection is correct? Why is the other one wrong?

Last edited: Nov 24, 2012
2. Nov 24, 2012

### grzz

If a light ray goes from one medium to a different medium along the normal the speed of light changes according to the ratio of the two media.

Also in this case of normal incidence there is no bending of the light ray and so the angles made by the light ray with the normal are both zero.

In investigating whether Snell's Law applies one has to be careful about any division by zero.

3. Nov 24, 2012

### sophiecentaur

If you wanted to find the refractive index using Snells Law then I can't see why you would want to use zero angles for your experiment. It would be as pointless as wanting to calculate the speed of an object by finding the time for it to move by a zero distance.
0/0 is not determinate.