QA for index of refraction

How do I find this index of refraction?

I know how to find the angle of refraction, but I don't know how to find the index.
Here's the question;
"A ray of light has an angle of incidence of 36.0 degrees on a block of quartz and an angle of refraction of 20.0 degrees. What is the index of refraction for the block of quartz?"
I think I read somewhere that quarts refracts at 1.458, but I don't know how to work out the question.

Answer:

refractive index = sine(incident angle)/sine(refractive angle)
=(sin 36)/(sin 20) =1.719
this does not match with experimental data because question may have been formed arbitrarily

How do you find the index of refraction of the material?

A beam of light of wavelength 553 nm travel-ing in air is incident on a slab of transparent
material.
Given: The incident beam makes an angle of 48.1 ◦ with the normal, and the refracted beam makes an angle of 26.3 ◦ with the nor-mal.
Find the index of refraction of the material.

Answer:

Use Snell's Law with n1 = 1
so 1*sin(48.1) = n2*sin(26.3)
So n = sin(48.1)/sin(26.3) = 1.68

How do you use refraction index to explain this experiment?

My teacher put a clear test tube in some refractory fluid, and you couldn't see it. All i know is that it has something to do with the refraction index. i don't know how to explain how the refraction index played a role in this. Can someone explain this to me, and why?

Answer:

Let's look at a similar case. If you have eyeglasses, the lenses are very very transparent, but they clearly bend light. We know the bending takes place at the interface between air and the lens material and the amount of bending depends on the different indices of refraction of the two materials (air and lens material). If you pop the lens out and hold it in your hand, you can still see it. But if you were to drop the lens into a liquid with the same index of refraction, there would be no bending (if you know snell's law, imagine that n1 and n2 are the same) of light. And the lens would 'vanish'. Optically, the lens is the same as the surrounding liquid.

 

How do you calculate the index of refraction of water?

The speed of light is 2.25 x 10^8 in water, how do I use this to find the index of refraction of water?

Answer:

The equation for index of refraction is:

n = (c/v)

So:

n = (3.00e8) / (2.25e8)
n = 1.33

Index of Refraction of Water

The index of refraction of a transparent medium is a measure of its ability to alter the direction of propagation of a ray of light entering it. If light were to travel through empty space and then penetrate a planar water surface, the measured angles of incidence and refraction could be substituted into Snell's Law (see "Refraction of Light by Water") to yield the index of refraction of water "relative to vacuum". The only variables would be those associated with the physical state of the water. But, in practice, it is simpler to conduct experiments using an air/water interface to obtain the index of refraction of water relative to air, and then to convert it from air to vacuum by applying appropriate corrections. The result, which is always greater than one, is the ratio of the phase velocity of light in a vacuum to its phase velocity in water: light travels more slowly in water than in a vacuum (or in air).

To various degrees, all transparent media are dispersive, which means that the amount by which they bend light varies with its wave length. Specifically, in the visible portion of the spectrum (approximately 4300-6900 Angstroms) the index of refraction is generally a decreasing function of wave length: violet light is bent more than red light. Furthermore, the rate of change of the index of refraction also increases as the wave length decreases. And, the index of refraction usually increases with the density of the medium. Water displays all of these characteristics. Table 1 shows the results of some measurements (Tilton and Taylor) of the index of refraction of water, n(w), with respect to dry air having the same temperature T as the water and at a pressure of 760 mm-Hg.

          
Table 1: Index of refraction of water as a 
function of wave length and water temperature. 
----------------------------------------------
  Wave Length                                   
   (Angstroms)   T=10 C   T=20 C   T=30 C        
                                              
      7065      1.3307   1.3300   1.3290         
      5893      1.3337   1.3330   1.3319         
      5016      1.3371   1.3364   1.3353         
      4047      1.3435   1.3427   1.3417         

To convert the tabulated values to indices relative to vacuum, add 4 to the fourth decimal place. Note that n(w) increases as the temperature of the water decreases. This is consistent with our expectations, since the density of water increases as it cools. It is interesting, however, that if the measurements are extended to lower temperatures the index does not show an anomaly at 4 degrees C, in spite of the fact that the water density peaks at that temperature.

Sea water contains dissolved impurities, primarily in the form of dissociated salts of sodium, magnesium, calcium, and potassium. Its density, and hence n(w), therefore depends on its salinity, a quantity usually expressed as grams of salts dissolved in a kilogram of sea water (gm/kg), or parts per thousand by weight. Table 2 (taken from Dorsey) shows how n(w) increases with salinity for the sodium D-lines (mean:5893 Angstroms) at 18 degrees C.

Table 2. Changes in index of refraction due to salinity 
--------------------------------------------------------
salinity                                                
(gm/kg)     increase in n(w)          example           
--------------------------------------------------------
   5            0.00097           northern Baltic Sea   
  10            0.00194                                 
  15            0.00290                                 
  20            0.00386           bight of Biafra       
  25            0.00482                                 
  30            0.00577                                 
  35            0.00673           Atlantic surface      
  40            0.00769           northern Red Sea      

The index of refraction is also a function of water pressure, but the dependence is quite weak because of the relative incompressibility of water. In fact, over the normal ranges of temperatures (0-30 C), the approximate increase in n(w) is 0.000016 when the water pressure increases by one atmosphere.
Clearly, the most significant factors affecting n(w) are the wave length of the light and the salinity of the water. Even so, n(w) varies by less than 1% over the indicated range of values of these variables. For most practical purposes it is sufficient to adopt the value n(w)=4/3.

The Speed of Light and the Index of Refraction

Have you heard these statements before? They are often quoted as results of Einstein's theory of relativity. Unfortunately, these statements are somewhat misleading. Let's add a few words to them to clarify. "Nothing can travel faster than the speed of light in a vacuum." "Light in a vacuum always travels at the same speed." Those additional three words in a vacuum are very important. A vacuum is a region with no matter in it. So a vacuum would not contain any dust particles (unlike a vacuum cleaner, which is generally full of dust particles).

Light traveling through anything other than a perfect vacuum will scatter off off whatever particles exist, as illustrated below.

In vacuum the speed of light is

c = 2.99792458 x 108 m/s

This vacuum speed of light, c, is what the statements from relativity describe. Whenever light is in a vacuum, its speed has that exact value, no matter who measures it. Even if the vacuum is inside a box in a rocket traveling away from earth, both an astronaut in the rocket and a hypothetical observer on earth will measure the speed of light moving through that box to be exactly c. No one will measure a faster speed. Indeed, c is the ultimate speed limit of the universe.

That's not to say that nothing ever travels faster than light. As light travels through different materials, it scatters off of the molecules in the material and is slowed down. For some materials such as water, light will slow down more than electrons will. Thus an electron in water can travel faster than light in water. But nothing ever travels faster than c. The amount by which light slows in a given material is described by the index of refraction, n. The index of refraction of a material is defined by the speed of light in vacuum c divided by the speed of light through the material v:
n = c/v

The index of refraction of some common materials are given below.

material	n	material	n
Vacuum	1	Crown Glass	1.52
Air	1.0003	Salt	1.54
Water	1.33	Asphalt	1.635
Ethyl Alcohol	1.36	Heavy Flint Glass	1.65
Fused Quartz	1.4585	Diamond	2.42
Whale Oil	1.460	Lead	2.6

Values of n come from the CRC Handbook of Chemistry and Physics

The values of n depend somewhat on wavelength, but the dependence is not significant for most applications you will encounter in this course. Unless you are told otherwise, assume the index of refraction given you is appropriate for the wavelength of light you are considering.

Those materials with large indices of refraction are called optically dense media. (A medium is just a fancy word for a type of material.) Materials with indices of refraction closer to one are called optically rare media. Being naturally lazy creatures, we generally drop the word "optical'' and talk about dense and rare materials. Just be careful not to confuse dense and rare in the optical context with mass density!
Notice that the index of refraction of air differs from the index of refraction of vacuum by a very small amount. For applications with less than 5 digits of accuracy, the index of refraction of air is the same as that of vacuum, n= 1.000. You will probably not encounter a situation in which the differenc between air and vacuum matters, unless you plan a future in precise optics experimentation.
Even though light slows down in matter, it still travels at an amazing speed, even through a dense material such as lead still travels at an amazing speed. (Although light does not travel far through lead before being absorbed, high-energy gamma rays can travel a centimeter or so through lead at the speed calculated here.) Using the definition of n, we can find the speed of light through lead:

v_lead = c/n_lead= (2.99792458 x 10⁸ m/s) /(2.6) = 1.2 x 10⁸ m/s = 2.6 x 10⁸miles per hour
Even slowed by lead, light travels at a speed of 260 million miles per hour! That's more than 10,000 times the speed of the orbiting space shuttle. (According to a NASA site, the space shuttle travels 17,322 miles per hour when in orbit.)

Refraction of Light by Water

Light entering or exting a water surface is bent by refraction. The index of refracton for water is 4/3, implying that light travels 3/4 as fast in water as it does in vacuum.

A measure of the extent to which a substance slows down light waves passing through it. The index of refraction of a substance is equal to the ratio of the velocity of light in a vacuum to its speed in that substance. Its value determines the extent to which light is refracted when entering or leaving the substance.

Refraction at the water surface gives the "broken pencil" effect shown above. Submerged objects always appear to be shallower than they are because the light from them changes angle at the surface, bending downward toward the water.

Refraction of Light

Refraction is the bending of a wave when it enters a medium where it's speed is different. The refraction of light when it passes from a fast medium to a slow medium bends the light ray toward the normal to the boundary between the two media. The amount of bending depends on the indices of refraction of the two media and is described quantitatively by Snell's Law.

The ratio of the speed of light in a vacuum to the speed of light in a medium under consideration. Also called refractive index.

Refraction is responsible for image formation by lenses and the eye.

As the speed of light is reduced in the slower medium, the wavelength is shortened proportionately. The frequency is unchanged; it is a characteristic of the source of the light and unaffected by medium changes.

What is Index of Refraction?

The index of refraction is defined as the speed of light in vacuum divided by the speed of light in the medium.

The indices of refraction of some common substances are given below with a more complete description of the indices for optical glasses given elsewhere. The values given are approximate and do not account for the small variation of index with light wavelength which is called dispersion.

Many materials have a well-characterized refractive index, but these indices depend strongly upon the frequency of light. Standard refractive index measurements are taken at yellow doublet sodium D line, with a wavelength of 589 nanometres.

There are also weaker dependencies on temperature, pressure/stress, et cetera, as well on precise material compositions (presence of dopants et cetera); for many materials and typical conditions, however, these variations are at the percent level or less. Thus, it is especially important to cite the source for an index measurement if precision is required.

In general, an index of refraction is a complex number with both a real and imaginary part, where the latter indicates the strength of absorption loss at a particular wavelength—thus, the imaginary part is sometimes called the extinction coefficient . Such losses become particularly significant, for example, in metals at short (e.g. visible) wavelengths, and must be included in any description of the refractive index.

Some representative refractive indices

Material	λ (nm)	n
Vacuum		1 (per definition)
Air at STP		1.000277
Gases at 0 °C and 1 atm
Air	589.29	1.000293
Carbon dioxide	589.29	1.00045
Helium	589.29	1.000036
Hydrogen	589.29	1.000132
Liquids at 20 °C
Arsenic trisulfide and sulfur in methylene iodide		1.9
Benzene	589.29	1.501
Carbon disulfide	589.29	1.628
Carbon tetrachloride	589.29	1.461
Ethyl alcohol (ethanol)	589.29	1.361
Silicone oil		1.52045
Water	589.29	1.3330
Solids at room temperature
Titanium dioxide (also called Titania or Rutile )	589.29	2.496
Diamond	589.29	2.419
Strontium titanate	589.29	2.41
Amber	589.29	1.55
Fused silica (also called Fused Quartz)	589.29	1.458
Sodium chloride	589.29	1.544
Other materials
Liquid helium		1.025
Water ice		1.31
Cornea (human)		1.373/1.380/1.401
Lens (human)		1.386 - 1.406
Acetone		1.36
Ethanol		1.36
Glycerol		1.4729
Bromine		1.661
Teflon		1.35 - 1.38
Teflon AF		1.315
Cytop		1.34
Sylgard 184		1.43
Acrylic glass		1.490 - 1.492
Polycarbonate		1.584 - 1.586
PMMA		1.4893 - 1.4899
PETg		1.57
PET		1.5750
Crown glass (pure)		1.50 - 1.54
Flint glass (pure)		1.60 - 1.62
Crown glass (impure)		1.485 - 1.755
Flint glass (impure)		1.523 - 1.925
Pyrex (a borosilicate glass)		1.470
Cryolite		1.338
Rock salt		1.516
Sapphire		1.762–1.778
Sugar Solution, 25%		1.3723
Sugar Solution, 50%		1.4200
Sugar Solution, 75%		1.4774
Cubic zirconia		2.15 - 2.18
Potassium Niobate (KNbO3)		2.28
Moissanite		2.65 - 2.69
Cinnabar (Mercury sulfide)		3.02
Gallium(III) phosphide		3.5
Gallium(III) arsenide		3.927
Zinc Oxide	390	2.4
Germanium		4.01
Silicon	590	3.96

The refractive index of a material is the most important property of any optical system that uses refraction. It is used to calculate the focusing power of lenses, and the dispersive power of prisms. It can also be used as a useful tool to differentiate between different types of gemstone, due to the unique chatoyance each individual stone displays.

Since refractive index is a fundamental physical property of a substance, it is often used to identify a particular substance, confirm its purity, or measure its concentration. Refractive index is used to measure solids (glasses and gemstones), liquids, and gases. Most commonly it is used to measure the concentration of a solute in an aqueous solution. A refractometer is the instrument used to measure refractive index. For a solution of sugar, the refractive index can be used to determine the sugar content.

Index of Refraction

In optics the refractive index (or index of refraction) n of a substance (optical medium) is a number that describes how light, or any other radiation, propagates through that medium.
Its most elementary occurrence (and historically the first one) is in Snell's law of refraction, n1sinθ1= n2sinθ2, where θ1 and θ2 are the angles of incidence of a ray crossing the interface between two media with refractive indices n1 and n2. Brewster's angle, the critical angle for total internal reflection, and the reflectivity of a surface also depend on the refractive index, as described by the Fresnel equations.

A measure of the extent to which a substance slows down light waves passing through it. The index of refraction of a substance is equal to the ratio of the velocity of light in a vacuum to its speed in that substance. Its value determines the extent to which light is refracted when entering or leaving the substance.

                                      Some representative refractive indices

Material	Index
Vacuum	1.00000
Air at STP	1.00029
Ice	1.31
Water at 20 C	1.33
Acetone	1.36
Ethyl alcohol	1.36
Sugar solution(30%)	1.38
Fluorite	1.433
Fused quartz	1.46
Glycerine	1.473
Sugar solution (80%)	1.49
Typical crown glass	1.52
Crown glasses	1.52-1.62
Spectacle crown, C-1	1.523
Sodium chloride	1.54
Polystyrene	1.55-1.59
Carbon disulfide	1.63
Flint glasses	1.57-1.75
Heavy flint glass	1.65
Extra dense flint, EDF-3	1.7200
Methylene iodide	1.74
Sapphire	1.77
Rare earth flint	1.7-1.84
Lanthanum flint	1.82-1.98
Arsenic trisulfide glass	2.04
Diamond	2.417

Recent research has also demonstrated the existence of the negative refractive index, which can occur if permittivity and permeability have simultaneous negative values. This can be achieved with periodically constructed metamaterials. The resulting negative refraction (i.e., a reversal of Snell's law) offers the possibility of the superlens and other exotic phenomena.