If light is moving from air into glass/water, in which case would light refract (bend) more? Is it true that water is denser than glass, so light bends more from air to water than from air to glass? By the way, does anyone know what are the physical and optical densities of water and glass? Can someone explain please?
By optical densities, i can only assume (someone correct me if im wrong) you are talking about the refractive index. Water=1.33 Air=1 Glass=1.3 to 1.7, or more/less, glass is highly flexible and can be commercialized to your desire (almost) sin(t1)*n1 = sin(t2)*n2 is the law of snell-descarte that links the angle of incidence to the angle of refraction. Application of this law should answer all your current and future question about refraction. This law is a specific application of fresnel equations which can both be deduced from the more general maxwell equations.
Suppose water and air Code: y | incident ray at angle t1 | / n1=1 | / | / |/ ----------------- x /| / | / | n2=1.33 / | / | refracted ray at angle t2 The angle is taken between y and the ray.
I see, so would light from air->glass (assume a normal one) be bent more or from air->water be bent more usually, given that the incident rays are at the same angle!
Is it because the index of refraction for glass (1.5?) is higher than that of water (1.33), so light form air->glass bent more? I search in google for physical densities for water and glass (accepted value in room temperature), but I am only able to find that for water and not the glass: Water's density is 1000 kg/(cubic cm) Does anyone know the accepted physical density for glass? Edit: I found and converted the density of glass: 0.002kg/(cubic cm) to 0.008kg/(cubic cm), which means density of glass is lower than that of water? Is this ture?
The density of glass depends significantly on which kind of glass you're talking about. Typical window or bottle glass has a density of about 2500 kg/m^3 or 2.5 g/cm^3. Source: http://hypertextbook.com/facts/2004/ShayeStorm.shtml Glass is an interesting substance because it is amorphous. The glass in your windows, for instance, is actually more of a liquid than a solid and can flow over long periods of time. The study of glassy phases is an interesting one because sometimes some of the rules of thermodynamics don't apply.
I am trying to compare density and refraction index: Water's density is 1 g/(cubic cm) [Edited] Glass' density is 2.5 g/(cubic cm) Water's refractive index is 1.33 Glass' refractive index is 1.5 And I found that water is much more densier than glass, but water's refractive index is lower than glass and light ray air->glass bent more than air->water...why?
Also, why is a liquid's (water) density higher than a solid's (glass) density? If I remember correctly, densities are generally: solid>liquid>gas
I think you've got the density of water wrong, kingwinner. The density of water is 1 g/cm^3 or 1000 kg/m^3 under normal conditions. This means glass has a density of 2.5 g/cm^3 and water has a density of 1 g/cm^3 i.e. glass is more dense.
I see, thanks for correcting me! Things get a lot clearer now! In my study notes got from my teacher, it says "because water is denser than glass, so light bends more from air->water than from air->glass" <-by now, I know that this is completely wrong and I must correct this now...(it really bugs me that the teacher is sending some wrong information to the students and this further confuses things...)
One more question, is there a realtionship between density and refractive index? For example, medium A and B, if medium A has a higher density, would it also have a higher refractive index? (for all cases?)
The relative mass densities of air/water/glass have nothing to do with the refractive index. The important thing is the electromagnetic properties, specifically the permittivity and permeability. These two properties combine to determine the speed of light in a given material (http://hyperphysics.phy-astr.gsu.edu/hbase/electric/elefie.html#c3). The refractive index is then the ratio of c to the speed of light in the material. The permeability of glass, water, and air are all pretty similar, but the permitivitty is what changes. This is an indication of how strong a dielectric a given material is. So basically the stronger the dielectric the higher the refractive index, regardless of mass density. Btw, I agree with Physics Monkey: the densities are incorrect. They should be on the same order. -Dale
DaleSpam, Welcome. While I agree that the density of a substance is not the only factor that determines the refractive index, I don't think it's totally unrelated. For example, the electric susceptibility of a dilute atomic gas in a weak field is proportional to the density of the gas. Of course, as you point out, substances with very similar densities can still have different indices of refraction due to other effects. What do you think?
Thanks for your welcome, Physics Monkey! I have just recently found the sciforums. You are probably right, they may not be completely unrelated. For example, water is a highly polar molecule, most non-polar molecules of similar molecular weight are gasses at STP. The strong polarity allows significant interaction (hydrogen bonds) which allows it to be a relatively dense liquid. The strong polarity is also what causes its high permittivity. So the two properties, electrical permittivity and mass density, may not be wholly unconnected in general. However, I sit here looking at these words through one particularly wonderful counter-example. My new "glasses" are actually made out of a relatively light-weight plastic, much less dense than my previous glasses (which were actually made of glass). Despite this lower mass density, the plastic has a higher refractive index than my previous glass lenses - and a much higher price Please Register or Log in to view the hidden image! I would expect that if we ran the tests we would determine that the plastic is a significantly better dielectric than the glass. In the end the permittivity and permeability of a material are what determine the speed of light within the material; and while mass density is probably strongly correlated, it is not the determining factor. -Dale
