Refraction of Light

REFRACTION OF LIGHT – 1 : REFRACTION OF LIGHT – 1 LECTURE BY: PROF. ARDAMAN SIDHU H.K.SIDHU INSTITUTE OF SCIENCES. hksidhuinstitute@gmail.com 09814123632 IN COLLABORATION WITH WIZIQ.COM

REFRACTION OF LIGHT – 1L8/AS 16thJuly,09 7.30p.m. : REFRACTION OF LIGHT – 1L8/AS 16thJuly,09 7.30p.m. REFRACTION REFRACTION THROUGH GLASS SLAB WHY SPOON IN WATER LOOKS BENT LENGTHNING OF DAY REFRACTION THROUGH COMPOUND SLAB. TOTAL INTERNAL REFLECTION. MIRAGE OPTICAL FIBRES BRILLIANCE OF DIAMOND TOTAL REFLECTING GLASS PRISMS

REFRACTION OF LIGHT : REFRACTION OF LIGHT Reflection of light is the phenomenon of change in the path of light, when it goes from one medium to another.

Slide 4 : The basic cause of refraction is change in the velocity of light in going from one medium to the other. V= ?? Frequency of light remains the same. Wavelength of light changes as it goes from one medium to another as a result velocity of light changes.

Laws of refraction : Laws of refraction The incident ray, the refracted ray and normal to the interface at the point of incidence, all lie in the same plane.

Laws of refraction : Laws of refraction The product of refractive index and sine of angle of incidence at a point in a medium is constant. This is called SNELL’S LAW.

SNELL’S LAW : SNELL’S LAW ? C1=Velocity of light in air or vacuum C2= Velocity of light in Medium Where represents refractive index of medium 2 w.r.t. medium 1. This law is called Snell’s Law

REFRACTION OF LIGHT THROUGH A RECTANGULAR GLASS SLAB : REFRACTION OF LIGHT THROUGH A RECTANGULAR GLASS SLAB ABCD is a rectangular glass slab. A ray of light is incident on the face AB of the slab at It is refracted along LM at   or …(1) Again applying Snell’s law at M. …(2)

Principle of reversibility of light : Principle of reversibility of light It states, when final path of a ray of light after any number of reflections and refractions is reversed, the ray retraces its centre path. Imagine a plane mirror P held normal to MN so that path MN is reversed. The ray would retrace its entire path. For the reversed ray, application of Snell’s law at M gives …(3) Multiplying (2) and (3), we get

The emergent ray is parallel to the incident ray : The emergent ray is parallel to the incident ray ?From (1) and (3) …(4) From (4), Hence the emergent ray MN is parallel to the incident ray KL.

EXPRESSION FOR LATERAL DISPLACEMENT. : EXPRESSION FOR LATERAL DISPLACEMENT. From M, draw MN’ KL produced Then MN’ is lateral displacement. This is the expression for lateral displacement.

REAL DEPTH AND APARENT DEPTH : REAL DEPTH AND APARENT DEPTH A water tank appears shallower i.e. less deep than what it actually is. This is on account of refraction of light.

REAL DEPTH AND APPARENT DEPTH OF A TANK : REAL DEPTH AND APPARENT DEPTH OF A TANK To prove this, suppose O is a point object at an actual depth OA below the free surface of water XY in a tank, Fig. A ray of light from O incident at ?i on XY, along OB deviates away from normal. It is refracted at ?r along BC. On producing back, BC meets OA at I. Therefore, I is virtual image of O i.e. when seen through water, O appears at I. Therefore, apparent depth = AI, which is less than the real depth OA.

REAL DEPTH AND APPARENT DEPTH : REAL DEPTH AND APPARENT DEPTH For all your Physics Problems Call me at……………9814123832 Email ………………. hksidhuinstitute@gmail.com

REFRACTION EFFECTS AT SUN RISE AND SUN SET : REFRACTION EFFECTS AT SUN RISE AND SUN SET The sun is visible to us before actual sun rise and after actual sun set. This is because of atmosphere refraction of light.

REFRACTION EFFECTS AT SUN RISE AND SUN SET : REFRACTION EFFECTS AT SUN RISE AND SUN SET The rays from the sun (S) coming through space enter earth’s atmosphere and travel from rarer to denser medium. They bend very slightly towards normal and appear to come from S’, the apparent position of sun. Therefore, the sun appears above the horizon. Hence the sun appears to rise a few minutes before the actual rise and for the same reason, it continues to be seen a few minutes after it has actually set. This time difference is of the order of 2 minutes each. Hence the day becomes longer by about 4 minutes due to refraction effects.

TOTAL INTERNAL REFLECTION OF LIGHT : TOTAL INTERNAL REFLECTION OF LIGHT We may define total internal reflection as the phenomenon of reflection of light into a denser medium from an interface of this denser medium and a rarer medium.

CONDITIONS FOR TOTAL INTERNAL REFLECTION : CONDITIONS FOR TOTAL INTERNAL REFLECTION Two essential conditions for total internal reflection are: Light should travel from a denser medium to a rarer medium. Angle of incidence in denser medium should be greater than the critical angle for the pair of media in contact.

TOTAL INTERNAL REFLECTION OF LIGHT : TOTAL INTERNAL REFLECTION OF LIGHT We may define critical angle for a pair of media in contact as the angle of incidence in the denser medium corresponding to which angle of refraction in the rarer medium is 90°.

TOTAL INTERNAL REFLECTION OF LIGHT : TOTAL INTERNAL REFLECTION OF LIGHT Hence we conclude that when a ray of light traveling from an optically denser medium to an optically rarer medium is incident at an angle greater than the critical angle for the pair of media in contact, the ray is totally reflected back into denser medium.

TOTAL INTERNAL REFLECTION OF LIGHT : TOTAL INTERNAL REFLECTION OF LIGHT Relation between Refractive index and Critical angle When I = C, r = 90° Applying Snell’s law at

APPLICATIONS OF TOTAL INTERNAL REFLECTION : APPLICATIONS OF TOTAL INTERNAL REFLECTION 1. The brilliance of diamond is due to total internal reflection of light, ? for diamond is 2.42, so that critical angle for diamond air interface as calculated from is 24.4°.

The brilliance of diamond : The brilliance of diamond The diamond is cut suitably so that light entering the diamond from any face falls at an angle greater than 24.4; suffers multiple total internal reflections at the various faces, and remains within the diamond. Hence the diamond sparkles.

APPLICATIONS OF TOTAL INTERNAL REFLECTION : APPLICATIONS OF TOTAL INTERNAL REFLECTION 2. Mirage is an optical illusion which occurs usually in deserts on hot summer days. The object such as a tree appears to be inverted, as if the face is on the bank of pond of water.

Mirage : Mirage On a hot summer day, temperature of air near the surface of earth is maximum. The upper layers of air have gradually decreasing temperature. Therefore, density and refractive index of air goes on increasing slightly with height above the surface of earth. At a particular layer, when angle of incidence becomes greater than the critical angle, total internal reflection occurs, and the totally reflected ray reaches the observer

APPLICATIONS OF TOTAL INTERNAL REFLECTION : APPLICATIONS OF TOTAL INTERNAL REFLECTION 3. Totally reflecting glass prisms. Totally reflecting glass prisms are right angled isosceles prisms which turn the light through 90° or 180°. They are based on the phenomenon of total internal reflection of light,? for glass is 1.5 so that critical angle for glass-air interface is 42°.

Totally reflecting glass prisms : Totally reflecting glass prisms In totally reflecting glass prisms, angle of incidence is made 45° (>C). Hence light suffers total internal reflection. This phenomenon is used in Binoculars

Totally reflecting glass prisms : Totally reflecting glass prisms This phenomenon is also used in Periscope For all your Physics Problems Call me at……………9814123832 Email ………………. hksidhuinstitute@gmail.com

APPLICATIONS OF TOTAL INTERNAL REFLECTION : APPLICATIONS OF TOTAL INTERNAL REFLECTION Optical fibers. These are also based on the phenomenon of total internal reflection. Optical fibers consist of several thousands of very long fine quality fibers of glass or quartz.

Optical fibers. : Optical fibers. The diameter of each fiber is of the order of 10-4 cm with refractive index of material being of the order of 1.5. The fibers are coated with a thin layer of material of lower refractive index of the order of 1.48.

Optical fibers. : Optical fibers. Light incident on one end of the fiber at a small angle passes inside and undergoes repeated total internal reflections inside the fiber. It finally comes out of the other end, even if the fiber is bent or twisted in any form. Fig. Shown.

Optical fibers. : Optical fibers. Applications of optical fibers A bundle of optical fibers is called light pipe. Optical fibers are used in transmission and reception of electrical signals by converting them first into light signals. Optical fibers are used in telephone and other transmitting cables. Each fiber can carry up to 2000 telephone messages without much loss of intensity.

Optical fibers. : Optical fibers. In medical field fibre optics are used in endoscopy and laparoscopy

Slide 34 : For all your Physics Problems Call me at……………9814123832 Email ………………. hksidhuinstitute@gmail.com