II PUC 2012 II PUC 2012 II PUC 2012 II PUC 2012 VIKASANA VIKASANA VIKASANA VIKASANA

SUBJECT PHYSICSSUBJECT PHYSICSSUBJECT : PHYSICSSUBJECT : PHYSICS

TOPIC : PHYSICAL OPTICSTOPIC : PHYSICAL OPTICS

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1. 1. Theories of light Theories of light -- 1 hr 1 hr 2 2 I t fI t f 3 h 3 h 2. 2. InterferenceInterference -- 3 hr 3 hr 3. 3. Diffraction Diffraction -- 3 hr 3 hr 4. 4. PolarisationPolarisation -- 4 hr 4 hr 5. 5. Speed of light Speed of light -- 1 hr 1 hr 5. 5. Speed of light Speed of light 1 hr 1 hr

Total Total -- 12hr 12hr -- 18 marks18 marksTotal Total -- 12hr 12hr -- 18 marks18 marks

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BLUE PRINTBLUE PRINTBLUE PRINTBLUE PRINT

PART PART –– AA -- 3 Questions 3 Questions PART PART AA 3 Questions 3 Questions TotalTotal -- 3 mark3 mark

PART PART –– BB -- 3 Questions3 QuestionsPART PART BB 3 Questions3 QuestionsTotal Total -- 6 mark 6 mark

PART PART –– CC -- 1 Question 1 Question PART PART CC 1 Question 1 Question (Q.No.24)(Q.No.24)TotalTotal -- 5 mark5 markPART PART –– DD -- 1 1 ProblemProblemPART PART DD 1 1 ProblemProblem(Q.No.39 or 40A)(Q.No.39 or 40A)Total Total --4 mark4 markTotal questions 8Total questions 8

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qqTotalTotal -- 18 mark18 mark

Introduction to theories of lightIntroduction to theories of lightand and speed of lightspeed of light : : and and speed of lightspeed of light : :

1 mark questions1 mark questions

1. Who proposed …….theory?1. Who proposed …….theory?

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Theories of LightTheories of LightNewton’s Corpuscular theory Newton’s Corpuscular theory Newton s Corpuscular theory Newton s Corpuscular theory (1675)(1675)Christian Christian Huygen’sHuygen’s Wave theory Wave theory Christian Christian Huygen sHuygen s Wave theory Wave theory (1678)(1678)Maxwell’s Electromagnetic theory Maxwell’s Electromagnetic theory Maxwell’s Electromagnetic theory Maxwell’s Electromagnetic theory (1864)(1864)Max Planck’s Quantum theory Max Planck’s Quantum theory (1901)(1901)

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( )( )

2. Mention any one draw back / 2. Mention any one draw back / failure or why a particular failure or why a particular theory is failed?theory is failed?theory is failed?theory is failed?

3 Name the physicist who 3 Name the physicist who 3.Name the physicist who 3.Name the physicist who experimentally detected experimentally detected electromagnetic waves electromagnetic waves electromagnetic waves. electromagnetic waves.

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4.What is meant by a wave front?4.What is meant by a wave front?

It is locus of all points vibrating It is locus of all points vibrating ith hith hwith same phase.with same phase.

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Electromagnetic Wave

5.What is the rest mass of photon?photon?

6. What is the value of speed of li ht bt i d i Mi h l ’ light obtained in Michelson’s rotating mirror Experiment ?

(2.99797 X 108 ms-1)7. Why Michelson’s rotatingy g

mirror is regarded as ‘null’ method?

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method?

8 Gi th f l f d f 8. Give the formula for speed of light in Michelson’s experiment

when rotating mirror with 12 faces is used.

C = 12nd C = 12nd

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9.Draw a neat diagram of 9.Draw a neat diagram of Michelson’s rotating mirror experiment.experiment.

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Michelson’s Rotating

Mirror Experiment

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TWO MARK QUESTIONSTWO MARK QUESTIONS

1. Write any two theories that support wave nature of light.pp g

2. Mention any two importance of y pspeed of light.

l b l d d f 3. Draw a neat labeled diagram of Hertz’s experiment.

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H t E i tHertz Experiment

P li h d b k bPolished brass knobs

60 cm

3 cm

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ONE / TWO M k Q tiONE / TWO Mark Questions

1 Wh t i i t f f li ht?1.What is interference of light?

It is the phenomenon of redistribution of light energy or g gymodification in the intensity of light due to the superposition of light due to the superposition of two are more similar light waves.

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2.What are coherent sources?

Two sources of light are said to gbe ‘coherent’, if they emit waves of same frequency of same frequency (or wavelength) and are either in phase or have a constant initial phase or have a constant initial phase difference.

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3.What is constructive / d t ti i t f ?destructive interference?

4.Write condition for constructive / destructive interference.

i) in terms of path difference andi) in terms of path difference andii) in terms of phase difference..

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C t ti I t fConstructive Interference

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Destructive Interference

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5. What are interference fringes? fringes?

6 Define fringe width6. Define fringe width.

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7 Gi th i f f i 7.Give the expression for fringe width in the Young’s double slit

i t d l i th experiment and explain the symbols.

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λ = wavelength of light used,

D = distance between the slit D = distance between the slit and the screen,

d = distance between thed distance between thetwo slits.

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8 W it t diti 8.Write any two conditions for obtaining sustained interference pattern.

1 Two sources must be 1. Two sources must be coherent sources of light.

2. Two sources of light should emit light waves continuously.

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3. Two coherent sources of light gshould be close to each other.

4. The amplitudes of the two waves should be equal for b better contrast.

5 Two coherent sources of light 5. Two coherent sources of light should be very narrow.

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6. The distance of the screen from the coherent sources of from the coherent sources of light should not be small.

7. The light should be monochromaticmonochromatic.

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9.What are Newton’s rings?When the Plano convex lens is kept pon the plane glass plate is viewed by illuminating with the light of y g gsuitable wavelength, due to the super position of reflected and super position of reflected and transmitted light, a interference pattern consisting of alternate pattern consisting of alternate bright and dark rings are produced. These are called Newton’s rings

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These are called Newton s rings.

10. Draw a neat sketch of the10. Draw a neat sketch of the

Newton’s rings apparatus.

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FIVE Mark QuestionsQ1. Give the theory of interference.

C id t i l h i C id t i l h i Consider two simple harmonic Consider two simple harmonic light waves,light waves,yy = a sin = a sin ωωt (1)t (1)yy11 = a sin = a sin ωωt ............…..(1)t ............…..(1)yy22 = b sin (= b sin (ωωt + t + φφ) …….(2)) …….(2)

According to the principle ofAccording to the principle ofsuper position of waves, super position of waves, The resultant displacement is, The resultant displacement is, y = yy = y11 + y+ y22

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Y= R sin(ω t + θ)Y= R sin(ω t + θ)

R resultant amplitude

The resultant displacement is also simple harmonicis also simple harmonic

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Amplitude of the resultant wave is given by

R = φcos222 abba ++

Resultant intensity at any point on the screen is given bypoint on the screen is given by

I I I 2 Ф III = Ia + Ib + 2 cosФ, (since I α|R2|)ba II

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Conditions for Constructive I fInterference

• I is maximum, when cosФ = +1

• or Ф = 0, 2π, 4 π, 6 π ………..

I l Ph • In general Phase

difference = Ф =2n πdifference Ф 2n π• where n = 0,1,2,3……… an integer

or the corresponding path difference• or the corresponding path difference.

λπλφλ nn2x33

λππ

φπ

nn === 222

x

Conditions for Destructive I t fInterference

• I is minimum, when cosФ = -1

• or Ф = π, 3 π, 5 π ……….. Etc.

• In general Phase difference • In general Phase difference,

Ф = (2n+1) π( )

• where n = 0,1,2,3……… an integer• or the corresponding path difference• or the corresponding path difference.

λπλφλ )12()12( +=+==

nnx34

λππ

φπ 2

)12(22

=+== nx

2. Obtain the expression for pfringe width in case of

Young’s double slit experiment.g p

Dark and bright bands in the interferenceDark and bright bands in the interferencepattern are called interference fringespattern are called interference fringespattern are called interference fringes.pattern are called interference fringes.Path difference between the waves emittedPath difference between the waves emittedby B and A and meeting at P isby B and A and meeting at P isby B and A and meeting at P isby B and A and meeting at P is∆∆y = y = BBP P –– APAP

and and ∆∆y = y =

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Bright fringes : (constructiveg g (interference/intensity maxima)

At any point on screen, I becomes

Dλmaximum, If = nλ or x =

dDnλ

is the position of nth bright fringe p g gfrom the central bright fringe.

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If n =1, x1 = dDλ

distance of the 1 bright fringe from the central maximum from the central maximum

If 2 Dλ2If n = 2, x2 = dDλ2

Fringe width β = x2 – x1= dDλ

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ONE / TWO Mark QuestionsONE / TWO Mark Questions

1 Wh t i diff ti f li ht ?1. What is diffraction of light ?

It is the phenomenon of bending of light around corners of small obstacles and hence it’s encroachment into the region of ggeometrical shadow.

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2. Distinguish between Fresnel’s 2. Distinguish between Fresnel s and Fraunhoffer’s diffraction.

F l’ • Fraunhoffer’s • Fresnel’s Diffraction

• Fraunhoffer’s Diffraction

1. The source and the screen

1. The source and the screen and the screen

are at finite distance from

are at infinite distance from distance from

the slit. the slit.

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• Fresnel’s Diffraction

• Fraunhoffer’s Diffraction

2. The wave 2 The wave front front is spherical or

2. The wave front is plane.

spherical or cylindrical.

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• Fresnel’s Diffraction

• Fraunhoffer’s Diffraction

3. Convex lens is 3 One or Two not required.

4 M th ti l

3. One or Two convex lens is required4. Mathematical

analysis is l

required.4. Mathematical

l i i complex. analysis is simple.

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Wh i h l i f 3. What is the resolving power of an optical instrument ?

It is the ability of the optical It is the ability of the optical instrument to distinguish the two closely lying point objects distinctlyclosely lying point objects distinctly.

Th i l f l i The reciprocal of resolving power is called limit of resolution.

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4. Define limit of resolution of telescope .telescope .

The limit of resolution of a The limit of resolution of a telescope is the minimum angular separation between angular separation between two closely lying point object s th t b di ti tl that can be seen distinctly.

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4. Define limit of resolution of microscopemicroscope

Limit of resolution of the Limit of resolution of the microscope is the minimum linear separation between two closely laying point object that y y g p jcan be seen distinctly.

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5. Write the expression for (i) Resolving power of telescope and (ii) Microscope and explain the symbols.

Resolving power of telescope:

Resolving power = = λ22.1

aθd1

a diameter of the aperture

λ wave length of light

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g g

Resolving power of microscope:Resolving power of microscope:Resolving power of microscope:Resolving power of microscope:

F l i For a non luminous source ,

θsin21 nResolving power =

λθsin21 n

d=

nsin θ is called numerical aperture.For a self luminous source , For a self luminous source ,

Resolving power =θsin21

=47

Resolving power = λ22.1=

d

6 E l i R l i h’ it i6.Explain Rayleigh’s criteria.

Rayleigh ‘s criterion for resolving y g gpower of optical instrument:

According to Rayleigh, two near by images are said to be resolved if gthe position of the central maximum of one coincides with the first of one coincides with the first secondary minimum of the other and vice versa

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and vice versa.

Rayleigh’s CriteriaRayleigh’s Criteriay gy g

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FIVE Mark QuestionsFIVE Mark Questions

1.What is Fraunhoffer’s diffraction ? Describe an experiment to produce Fraunhoffer’s diffraction at a single slit.g

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Fraunhofer diffractionFraunhofer diffractionat a single slit:

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The Path difference betweenthe secondary waves arriving

on the screen = dsinөon the screen = dsinөCondition for minima:

dsinө = n λwhere n = 0 1 2 Is an where, n = 0,1,2,…. Is an

integer53

g

Condition for maximaCondition for maxima

d i (2 1) λ /2dsinө = (2n+1) λ /2where, n = 0,1,2,…. is an where, n 0,1,2,…. is an

integer

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ONE / TWO Mark Questions/ Q1.What is polarization ?

It i th h f t i ti It is the phenomenon of restricting /confining the plane of vibration of light to one pa tic la plane

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light to one particular plane.

2. Methods of producing plane p g ppolarized light

i) Reflection

ii) Refraction

iii) Double Refraction

iv) Selective absorption

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3 Represent unpolarized and plane 3.Represent unpolarized and plane polarized light diagrammatically.

Unpolarized light

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4.What is meant by plane of 4.What is meant by plane of polarization / vibrationpolarization / vibration..pp

.

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• Plane of vibration is the plane containing the vibrations of plane polarized light.p p g

Pl f l i ti i th • Plane of polarization is the plane containing no vibrations

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5 Write any two difference 5.Write any two difference between E-ray and O-ray.

O-ray

1 It b S ll’

E-ray

1 It d t b 1. It obeys Snell’slaw of refraction

1. It does not obey Snell’s law of refraction in all refraction

in all directions.refraction in all directions.

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O-ray E-ray

2. The refractive index and speed

2. The refractive index and speed index and speed

of light is same in all directions

index and speed of light is different in in all directions. different in different directions.

6.What are H and K – polaraids?

H Polaroid : H-Polaroid : These are the Polaroid made up of stretched thin film of polyvinyl alcohol stained with Iodine.

They are brown in colour.They are brown in colour.

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K-polaroid :

These are the Polaroid made up pof a stretched film of polyvinyl alcohol heated with a suitable alcohol heated with a suitable dehydrating agent like HCl.They are colourlessThey are colourless.

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7.Write any two applications of 7.Write any two applications of polaroids.

Polaroid’s are usedPolaroid s are used

1 in laboratories to produce 1. in laboratories to produce and analyze plane polarized lightlight.

2. in photographic cameras asfilters to see 3-dimensional filters, to see 3 dimensional pictures,

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Polaroid’s are used

3. in wind shields of automobiles to avoid glare

4. in sunglasses

5 i h i d f 5. in the window panes of aero planes to

l i i f li hcontrol intensity of light.

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9.Define specific rotation of an optically active solution / solidoptically active solution / solid.

Specific rotation an optically active Specific rotation an optically active solution at a given temperature for a given wavelength of light is numerically given wavelength of light is numerically equal to the rotation produced by the solution of length 1m having unit solution of length 1m having unit concentration.

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Specific rotation of optically active Specific rotation of optically active solid at a given temperature for a

i l th f li ht i given wavelength of light is numerically equal to the rotation produced per mm thickness of the solid.

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11 Wh t i l l d 11.What are circularly and elliptically polarized light?

If the tip of the plane polarized light traces a circle then it is said to be traces a circle then it is said to be circularly polarized light.

If the tip of the plane polarized light traces an ellipse then it is said to be traces an ellipse then it is said to be elliptically polarized light.

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FIVE Mark Questions1. Define Brewster’s angle. Show

that the reflected and refracted rays are yperpendicular to each other when the angle of incidence is equal to the g qBrewster’s angle.

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Brewster's angle is the angle of incidence for which the

reflected light is completely plane polarized.plane polarized.

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It is clear from the figure that+ PôQ + r = 180 or+ r = 180 PôQ = 180 90+ r = 180 - PôQ = 180 - 90

= 90

⁂ r = 90 (1)⁂ r = 90 - (1)

From the Snell’s law we haveFrom the Snell’s law, we have

nn

but i = ⁂ n (2)

From (1) and (2) we get,

n = = tan

2.Define specific rotatory power p y pof an optically active solution. Describe the method of Describe the method of determining the specific rotatory power of sugar solution rotatory power of sugar solution by using Laurent’s half-shade

l i tpolarimeter.

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LAURENT’S HALF SHADE LAURENT’S HALF SHADE POLARIMETERPOLARIMETERPOLARIMETERPOLARIMETER

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