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Overview         (For age - group : Below 16 )

Light behaves very strangely when it passes through a medium different from air. This school science animation contains all laws, terminology, speed of light, car example, equations, 3d view etc. The science software is very useful for students who want to understand the concept behind refraction.

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Refraction of Light :

Category : Science

Type : Animation (advanced)

Length : 16 minutes

The e-learning software contains the following

  • Tracing the path of a light ray through a rectangular glass block
  • Properties of optically denser and rarer medium
  • Common terms animated : Incident ray, normal and refracted ray, angle of incidence and refraction, Index of refraction
  • Analogy to understand the refraction of light
  • First law of refraction (Snell's law)
  • Second law of refraction
  • Cases in refraction
  • Lateral displacement
  • Principle of reversibility of light
  • Total internal reflection and critical angle

Explanatory notes contain :

  • Why the upper surface of water in a beaker and held above eye level appears silvery ?
  • Why an empty test tube held obliquely in water and seen from above seems silvery ?

refraction of a beam of light through a glass block
incident, refracted ray and normal
Refraction of a beam of light through a glass block
Incident, refracted ray and normal
total internal reflection
Analogy of refraction to a car
Total internal reflection
Analogy of refraction to a car moving from road to gravel
Details of the animation/ movie /software

As light travels through a given medium, it travels in a straight line. However, when light passes from one medium into a second medium, the light path bends; this bending of light rays is known as refraction. The refraction occurs only at the boundary. Refraction can be better understood through the analogy of car moving from concrete road onto a sandy track.

The relation between the angle of incidence and angle of refraction is given by Snell's law:

µ= sin i / sin r. This ratio gives the refractive index of the second media with respect to the first.

Once the light has crossed the boundary between the two media, it continues to travel in a straight line; only now, the direction of that line is different than it was in the former medium. If when sighting at an object, light from that object changes media on the way to your eye, a visual distortion is likely to occur. This visual distortion was witnessed in The Bent Pencil. The ray traveling back to the medium 1 is laterally displaced. The refracted ray follows the principle of reversibility i.e. it retraces the same path while coming back from the medium 2 to medium 1.

If the rays traveling from a denser medium to a rarer medium are incident at an angle greater than the critical angle for the pair of media, the rays are reflected back into the medium 1 from the boundary rather than being refracted to another medium. This principle is aptly utilized in optical cables.

If you are still unclear about the concepts, please refer the animation

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Q & A
Q1: what will be the reverse path of the light when travelling from denser to rarer medium and creates a refraction of 90' from the normal Ancoor 29/9/2013
Q2: why there is no phase change in refraction,but phase changes by pi in case of reflection from denser medium? Surbhi 5/2/2013
Q3: Which principle of light is used in vision Barbie 4/10/2010
Q4: why we can't see the sound waves. M ASMAR 30/9/2010
Q5: why light can't refrect when enter parallal to the normal. M ASMAR 30/9/2010
Q6: is the intensity of light reduced when it passes into another medium?. hosea joseph bulashi 6/7/2010
Q7: how does light rays behave when it pass from air and water? nino 5/7/2010
Q8: Why does light refract towards the normal as it passes from rare medium to optically dense medium? why not away from the normal? Amaha Araya 13/3/2010
Q9: Which two materials provide the most refraction of light vikkii 31/3/2009
Q10: is the principle of optical reversibility posiible in the case of total internal reflection of light anil pillai 8/9/2008
Q11: when light falls perpendicular to glass slab why refraction doesnt take place while it is changing its medium as well? And on changing medium speed also changes,why this happens? tooba 16/7/2008
Q12: Why there is no refraction when light falls perpendicular to glass slab? AJIALEX 21/6/2008
Q13: A person is able to see objects clearly only when these are lying at distances between 50cm and 300cm from his eye.What kind of defects of vision he is suffering from/ AJIALEX 21/6/2008
Q14: why refraction doesnot takes place in normal incidence? i want an answer in physical sence, not in the mathematical sence. girisn 22/5/2008
Q15: A ray of light enters from a rarer to denser medium, the angle of incidence is 'i' then the reflected and the refracted rays are mutually perpendicular to each other. The critical angle for the pair of media."Is this question valid ?" Vivek 20/4/2008
Q16: why total internal reflection cannot take place when light travelling through a rarer medium enters a denser medium? hamza 10/3/2008
Ans: When light travels from a rarer to denser medium it bends towards the normal, the condition for total internal reflection requires the ray to bend away from the normal till 90 degree angle is attained. In the rarer to denser case if the incident ray is at 0 degree ( parallel to normal) the refracted ray is also at 0 that mean it is passing straight through, at 90 degree angle of incident ray there will total internal reflection but then incident ray is actually not passing through rarer medium. Hence it will not be a case of rarer to denser medium refraction.
Q17: An old lady can not read a book kept at 25 cm. Which defect of eye is she suffering from? I asked this question earlier. As the lady is old, can she be suffering from presbyopia (due to gradual weakening of ciliary muscles & hence inability to read)? pankhuri 25/1/2008
Ans: Okay here goes. The problems could be 1) Cornea, this smooth surface can be damaged by conditions such as blepharitis, an inflammation of the eyelids. More serious symptoms can also occur due to evaporation of the tears and drying out of the corneal surface. This is known as dry eyes. 2) Lens : The lens is also subject to the aging process, and the resulting conditions--cataracts and presbyopia. The clouding of the lens--or cataract—results in diminished vision. A hardened lens becomes more fixed on distant objects and cannot focus as well on nearby objects or vice versa, this is known as presbyopia. 3) Retina : Macular degeneration (loss of central retinal function) and glaucoma (damage to the optic nerve due to increased intraocular pressure) can also take place.
Q18: An old lady can not read a book kept at 25 cm. Which deffect of eye is she suffering from? pankhuri 23/1/2008
Ans: Hyperopia, or farsightedness
Q19: What is the power of accomodation of a healthy human eye? pearl 23/1/2008
Ans: The ability of the eye to adjust its focal length is known as accommodation. The eye accommodates by assuming a lens shape that has a shorter focal length. A healthy eye is able to bring both distant objects and nearby objects into focus without the need for corrective lenses. The maximum variation in the power of the eye is called the Power of Accommodation. A young human eye can change focus from distance to 7 cm from the eye in 350 milliseconds. This dramatic change in focal power of the eye of approximately 15 diopters.
Q20: what is an emergent ray,refracted ray, angle of incidence and angle of refraction? jane 15/9/2007
Ans: Hi Jane, you need to refer some basic book on light, ours is not a homework help site but a concept help site, I will be glad to help you with your concepts and with understanding theory but not with basic definitions that you can find in any textbook or websites. Do revert with your confusions, problems and be assured we will assist you. All the best - Admin
Q21: analogy between refraction and a car moving from road onto marshy land zaynah 15/8/2007
Ans: A car moving along the road turns into the sidewalk of gravel or sand, the wheel first meeting the sand slows down due to resistance but the second wheel is still moving at the same speed as it is on the road, hence the car experiences a turning motion or change in angle. Once all wheels are in sand the car moves in a straight line again
Ans: Air water – 35.2 degrees, please use Snell’s law to calculate the angle of refraction for other mediums example air glass, air oil, air diamond or a combination of these
Q23: Does the lateral displacement of light increase as its angle of incidence increases? kay 12/2/2007
Ans: Yes it does, lateral displacement is directly proportional to angle of incidence, it tends to maximum as angle of incidence approaches 90 degree.
Q24: do all wavelengths,green,red,indigo travel at constant speed in air or vacum? mihir 12/11/2006
Ans: Yes and no, all electromagnetic radiations (including colors of light) travel at the same speed in vacuum, but in air or any other medium the speeds are different (or they undergo refraction), the denser a medium is the higher will be the reduction in speed and more prominent will be the refraction, this is why dispersion is prominent when light is passed thru a glass prism, a highly dense medium but is not at all prominent when it passes thru a rare medium like air.
Q25: why does the light ray bend towards the normal when travels from rarer medium to denser medium? suhas 21/9/2006
Ans: Bending of light due in refraction is primarily due to change in speed of its wavefront when it meets a different medium. The part closer to medium slows down causing a bending.
Q26: what is lateral displacement on plane refractors? hart 12/9/2006
Ans: A ray of light emerges out a glass slab in a direction parallel to its entry but displaced in the x direction due to refraction. This is the lateral (horizontal) displacement. This mainly happens because of parallel faces of a glass slab, if the glass slab’s second face was not parallel the light would disperse into its component colors as it does in a prism.
Q27: what is a light? sajjadh 4/4/2006
Ans: The answer for this will not satisfy you because it could be simple one like light is an electromagnetic radiation with its wavelength lying in the visible range or could be complicated enough to spill beyond tomes if one were to cover its nature, properties, sources, measurement. There have been many theories written about it and frankly speaking till this day it is still somewhat a mystery.
Q28: what is cauchy's constant s.viji 1/4/2006
Ans: Cauchy’s constant are a part of dispersion for relationship between a wave length (lambda shown by #) of electromagnetic radiation and the corresponding refraction ratio n where n = a + b/#2+ c/#4 + ···, where a, b, c ··· are constants which characterize the substance and # represents the symbol lambda. Later these were shown to be close to dielectric constants by Helmholtz and kettler using a modified equation
Q29: what is gravity well? hari 25/3/2006
Ans: Spacetime is thought of as being bent by the presence of mass. This distortion in space-time caused by a massive body such as a planet is called a gravity or potential well. It extends to the surface of the body and has the shape of a four-dimensional paraboloid of revolution, symmetrical about the central mass. Anything on a planet or star is considered to be at the bottom of the gravity well, so to “climb” out of it, requires great energy. The larger a planet is deeper is its gravity well.
Q30: is it possible to build time machine? alisha 21/3/2006
Ans: Einstein's special theory of relativity allows time travel only in future using gravity well. Traveling back in time brings up Occam razor’s issues of causality, what will happen if you went back and killed your great-grandfather. The spacetime curvature caused by mass-energy and the flow of momentum may produce closed curves making back travel possible, there are many interesting theories out there but practically if someone went back in time, well we are still awaiting his return back…
Q31: when light can travel in vaccum why cant sound travel in vaccum? sonu 19/3/2006
Ans: Sound is composed of longitudinal waves (alternate compressions and expansions of matter) and in vacuum there is no matter available. Light is composed of transverse waves in an electromagnetic field. There are different views on light travel through vacuum light is considered like a wave and particle together, particles do not require medium. Another theory is it is electromagnetic in nature and has got more to do with one field generating the other so does not need medium
Q32: how does light travel? shaheen 9/3/2006
Ans: Light can travel in the form of electromagnetic radiation in any medium including vacuum
Q33: why the crital angle is 48.75 degrees? Alice 13/2/2006
Ans: Critical angles depend on material of medium, optically denser material (more electrons for collision) slow down the light, light speed in vacuum is 299,792 km/s, in air 299702 km/s, in water 225,000 km/s, in diamond 125,000 km/s. Relation is given by n= c/v; for air, n= 1.0003; for water n= 1.33. Hence n (air-water) = n(air)/n(water) = 1.0003/1.33= 0.752. Critical angle n = sin I(critical) / sin R since Sin R=Sin 90= 1; n = sin I(critical) ; since n = 0.752 therefore I(critical) = 48.75 deg
Q34: explain two laws of refraction madhur 9/2/2006
Ans: Refraction is due to a change in the speed of light as it passes from one medium to another, normally referred to as bending of light, if we take a wavefront of light , as it meets another medium the portion at one end meeting the medium first, slows down while another keeps on moving at the same speed causing a bending of wavefront to occur, once they enter the medium they move together again but with a new speed, the change in speed produces refraction.

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