# 0.1 Geometrical optics - grade 10  (Page 5/14)

 Page 5 / 14

When light travels from one medium to another, it will be bent away from its original path. When it travels from an optically dense medium like water or glass to a less dense medium like air, it will be refracted away from the normal ( [link] ). Whereas, if it travels from a less dense medium to a denser one, it will be refracted towards the normal ( [link] ).

Just as we defined an angle of reflection in the previous section, we can similarly define an angle of refraction as the angle between the surface normal and the refracted ray. This is shown in [link] .

## Refractive index

Which is easier to travel through, air or water? People usually travel faster through air. So does light! The speed of light and therefore the degree of bending of the light depends on the refractive index of material through which the light passes. The refractive index (symbol $n$ ) is the ratio of the speed of light in a vacuum to its speed in the material.

Refractive Index

The refractive index of a material is the ratio of the speed of light in a vacuum to its speed in the medium.

## Interesting fact

The symbol $c$ is used to represent the speed of light in a vacuum.

$c=299\phantom{\rule{0.277778em}{0ex}}792\phantom{\rule{0.277778em}{0ex}}485\phantom{\rule{0.166667em}{0ex}}\mathrm{m}·{\mathrm{s}}^{-1}$

For purposes of calculation, we use $3×{10}^{8}\phantom{\rule{0.166667em}{0ex}}\mathrm{m}·{\mathrm{s}}^{-1}$ . A vacuum is a region with no matter in it, not even air. However, the speed of light in air is very close to that in a vacuum.

Refractive Index

The refractive index (symbol $n$ ) of a material is the ratio of the speed of light in a vacuum to its speed in the material and gives an indication of how difficult it is for light to get through the material.

$n=\frac{c}{v}$

where

 $n$ = refractive index (no unit) $c$ = speed of light in a vacuum ( $3,00×{10}^{8}\phantom{\rule{0.166667em}{0ex}}\mathrm{m}·{\mathrm{s}}^{-1}$ ) $v$ = speed of light in a given medium ( $\phantom{\rule{0.166667em}{0ex}}\mathrm{m}·{\mathrm{s}}^{-1}$ )

## Refractive index and speed of light

Using

$n=\frac{c}{v}$

we can also examine how the speed of light changes in different media, because the speed of light in a vacuum ( $c$ ) is constant.

If the refractive index $n$ increases, the speed of light in the material $v$ must decrease. Light therefore travels slowly through materials of high $n$ .

[link] shows refractive indices for various materials. Light travels slower in any material than it does in a vacuum, so all values for $n$ are greater than 1.

 Medium Refractive Index Vacuum 1 Helium 1,000036 Air* 1,0002926 Carbon dioxide 1,00045 Water: Ice 1,31 Water: Liquid ( ${20}^{\circ }$ C) 1,333 Acetone 1,36 Ethyl Alcohol (Ethanol) 1,36 Sugar solution (30%) 1,38 Fused quartz 1,46 Glycerine 1,4729 Sugar solution (80%) 1,49 Rock salt 1,516 Crown Glass 1,52 Sodium chloride 1,54 Polystyrene 1,55 to 1,59 Bromine 1,661 Sapphire 1,77 Glass (typical) 1,5 to 1,9 Cubic zirconia 2,15 to 2,18 Diamond 2,419 Silicon 4,01

## Snell's law

Now that we know that the degree of bending, or the angle of refraction, is dependent on the refractive index of a medium, how do we calculate the angle of refraction?

what is Nano technology ?
write examples of Nano molecule?
Bob
The nanotechnology is as new science, to scale nanometric
brayan
nanotechnology is the study, desing, synthesis, manipulation and application of materials and functional systems through control of matter at nanoscale
Damian
Is there any normative that regulates the use of silver nanoparticles?
what king of growth are you checking .?
Renato
What fields keep nano created devices from performing or assimulating ? Magnetic fields ? Are do they assimilate ?
why we need to study biomolecules, molecular biology in nanotechnology?
?
Kyle
yes I'm doing my masters in nanotechnology, we are being studying all these domains as well..
why?
what school?
Kyle
biomolecules are e building blocks of every organics and inorganic materials.
Joe
anyone know any internet site where one can find nanotechnology papers?
research.net
kanaga
sciencedirect big data base
Ernesto
Introduction about quantum dots in nanotechnology
what does nano mean?
nano basically means 10^(-9). nanometer is a unit to measure length.
Bharti
do you think it's worthwhile in the long term to study the effects and possibilities of nanotechnology on viral treatment?
absolutely yes
Daniel
how to know photocatalytic properties of tio2 nanoparticles...what to do now
it is a goid question and i want to know the answer as well
Maciej
Abigail
for teaching engĺish at school how nano technology help us
Anassong
Do somebody tell me a best nano engineering book for beginners?
there is no specific books for beginners but there is book called principle of nanotechnology
NANO
what is fullerene does it is used to make bukky balls
are you nano engineer ?
s.
fullerene is a bucky ball aka Carbon 60 molecule. It was name by the architect Fuller. He design the geodesic dome. it resembles a soccer ball.
Tarell
what is the actual application of fullerenes nowadays?
Damian
That is a great question Damian. best way to answer that question is to Google it. there are hundreds of applications for buck minister fullerenes, from medical to aerospace. you can also find plenty of research papers that will give you great detail on the potential applications of fullerenes.
Tarell
what is the Synthesis, properties,and applications of carbon nano chemistry
Mostly, they use nano carbon for electronics and for materials to be strengthened.
Virgil
is Bucky paper clear?
CYNTHIA
carbon nanotubes has various application in fuel cells membrane, current research on cancer drug,and in electronics MEMS and NEMS etc
NANO
so some one know about replacing silicon atom with phosphorous in semiconductors device?
Yeah, it is a pain to say the least. You basically have to heat the substarte up to around 1000 degrees celcius then pass phosphene gas over top of it, which is explosive and toxic by the way, under very low pressure.
Harper
Do you know which machine is used to that process?
s.
how to fabricate graphene ink ?
for screen printed electrodes ?
SUYASH
What is lattice structure?
of graphene you mean?
Ebrahim
or in general
Ebrahim
in general
s.
Graphene has a hexagonal structure
tahir
On having this app for quite a bit time, Haven't realised there's a chat room in it.
Cied
how did you get the value of 2000N.What calculations are needed to arrive at it
Privacy Information Security Software Version 1.1a
Good
Berger describes sociologists as concerned with
Got questions? Join the online conversation and get instant answers!