PHYSICAL OPTICS. Ans: 1 Sol: The condition to form bright band at a point is to have a path difference of x = nλ From the given problem

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Esther Candice Banks
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1 PHYSCAL OPTCS PREVOUS EAMCET BTS (ENGNEERNG PAPER). n the Young s doule slit experiment the intensities at two points P and P on the screen are respectively and. f P is located at the centre of right fringe and P is located at a distance equal to a quarter of fringe width from P, then / is [EAMCET 009 E] ) ) / 3) ) 6 Ans: f a is the amplitude of one of the interfering wave then intensity at any point is given as φ = a cos.() φ At right fringe cos = = a..() π = a cos = a () () divided y () a = = a. n Young s doule slit experiment, the 0 th maximum of wavelength λ is at a distance of y from the central maximum. When the wavelength of the source is changed to λ, 5 th maximum is at a distance of y from its central maximum. The ratio (y / y ) is [EAMCET 009 E] λ λ λ λ ) ) 3) ) λ λ λ λ Ans: The condition to form right and at a point is to have a path difference of x = nλ From the given prolem y = 0λ () y = 5λ..() Dividing () and () y λ = y λ 3. Four light sources produce the following four waves : [EAMCET 009 E] i) y = asin( ω t+φ ) ii) y = asinω t iii) y3 = a sin( ω+φ t ) ) y = a sin( 3ω t+φ ) Superposition of which two waves give rise to interference? ) (i) and (ii) ) (ii) and (iii) 3) (i) and (iii) ) (iii) and (iv) Ans : 3 For otaining sustained interference pattern the sources should maintain same phase or constant phase difference i.e. the source should e coherent

2 . n Fraunhoffer diffraction experiment, L is the distance etween screen and the ostacle, is the size of ostacle and λ is wavelength of incident light. The general condition for the applicaility of Fraunhoffer diffraction is [EAMCET 008 E] ) >> ) = 3) =<< ) Lλ ) f >>, the approximation of geometrical optics is applicale ) f <<, Fraunhofer diffraction is oserved 3) Lλ, Fresnel diffraction is oserved 5. n Young s doule slit experiment, first slit has width four times the width of the second slit. The ratio of the maximum intensity to the minimum intensity in the interference fringe system is [EAMCET 006 E] ) : ) : 3) 9 : ) 8 : As ntensity width of the slit a or width of slit max + = min w + w = w w max + 9 = = min 6. A light ray of wavelength λ is passing through a pin hole of diameter D and the effect is oserved on a screen placed at a distance L from the pin hole. The approximations of geometrical optics are applicale if [EAMCET 005 E] L ) D ) λ L λ Lλ = 3) << ) >> D D D ) f >>, the approximation of geometrical optics is applicale ) f <<, Fraunhofer diffraction is oserved 3) Lλ, Fresnel diffraction is oserved 7. Consider the following statements A and B and identify the correct answer [EAMCET 00 E] A: Fresnel s diffraction pattern occurs when the source of light or the screen on which the diffraction pattern in seen or when oth are at finite distance from the aperture. B: Diffracted light can e used to estimate the helical structure of nucleic acids. ) A and B are true ) A and B are false

3 3) A is true ut B is false ) A is false ut B is true n Fresnels diffraction pattern the source and the screen are of finite distance. Polarisation is used to estimate the helical structure of nucleic acid. 8. n Young s doule slit experiment, an interference pattern is otained on a screen y a light of wavelength 6000 A coming from the coherent sources S and S. At certain point P on the screen third dark fringe is formed. Then the path difference SP SP in microns is [EAMCET 003 E] ) 0.75 ) 5 3) 3.0 ).5 Ans: The condition for dark fringe is λ path difference = (n + ) Δ x = ( + ) 6 =.5 0 m =.5 micron 9. Consider the following statements A and B. dentify the correct choice in the given answers: A : The refractive index of the extraordinary ray depends on the angle of incidence in the doule refraction. B: The viration of light waves acquire one sided ness for oth ordinary and extraordinary rays in doule refraction [EAMCET 00 E] ) A and B are wrong ) A and B are correct 3) A is correct B is wrong ) A is wrong B is correct Ans: n doule refraction method oth ordinary and extra-ordinary ray are polarised. The refractive index of the extra ordinary ray depends on the angle of incidence ut the refractive index of the ordinary ray is independent of angle of incidence. 0. n Young s doule slit interference experiment the wave-length of light used is 6000A. f the path difference etween waves reaching a point P on the screen is.5 microns, then at that point P. [EAMCET 00 E] ) Second right and occurs ) Second dark and occurs 3) Third dark and occurs ) Third right and occurs λ n The condition for dark and is path difference ( ) ( n ) = = 5 ; n = Third dark and occurs. Light waves producing interference have their amplitudes in the ratio 3 :. The intensity ratio of maximum and minimum of interference fringes is [EAMCET 00 E] ) 36 : ) 9 : 3) 5 : ) 6 : a 3 = [ given ] a max a + a 3+ 5 = = = = 5 min a a 3 3

4 . The difference in the numer of wavelengths, when yellow light propagates through air and vacuum columns of the same thickness, is one. The thickness of the air column is: (Refractive index of air μ a =.0003; Wavelength of yellow light in vacuum = 6000A ) [EAMCET 00 E] ).8 mm ) mm 3) cm ). cm Ans: MEDCAL 3. Four light sources produce the following four waves : [EAMCET 009 M] i) y = asin( ω t+φ ) ii) y = asin( ω t) iii) y3 = a sin( ω t+φ ) ) y = a sin( 3ω+φ t ) Superposition of which two waves give rise to interference? ) (i) and (ii) ) (ii) and (iii) 3) (i) and (iii) ) (iii) and (iv) The condition for interference is that two wave should have same phase or should maintain constant phase difference.. Two light eams produce interference pattern to give maxima and minima on the screen. f the intensities of the light eams are in the ratio of 9 :, then the ratio of intensities of maxima and minima is [EAMCET 009 M] ) 3 : ) 5 : 3) 5 : ) 9 : 9 = [ given ] a 9 a 3 = = = a a max a+ a 3+ 5 = = = = 5 min a a 3 5. Wave theory cannot explains the phenomena of [EAMCET 008 M] A) Polarization B) Diffraction C) Compton effect D) Photoelectric effect Which of the following is correct? ) A and B ) B and D 3) C and D ) D and A Wave theory explains the phenomena of polarization and diffraction ut the particle nature explains aout Compton effect and photo electric effect. 6. n Young s doule slit experiment using two identical slits, the intensity at a right fringe on the screen is. f one of the slits is now closed, the intensity of the same right fringe on the screen will e [EAMCET 008 M] ) ) 3) ) Ans: Let a is the amplitude of the interfering wave. = ( a ) ( ) + a = a+ a = a f one slit is closed

5 5 Physical Optics ( ) = a = 7. The source is at some distance from an ostacle distance etween ostacle and the point of oservation is and wavelength is λ. Then the average distance of n th Fresnel zone will e at a distance - from the point of oservation [ EAMCET 007 M] ) n λ nλ nλ ) 3) + ) nλ f the distance etween ostacle and the point of oservation is then the distance of n th Fresnel nλ Zone = + from the point of oservation. 8. Two coherent monochromatic light sources are located at two vertices of an equilateral triangle. f the intensity due to each of the sources independently is Wm at the third vertex. The resultant intensity due to oth the sources at that point (i.e., at the third vertex) is (in Wm ) [EAMCET 006 M] ) Zero ) 3) ) Ans: = = watt/m Phase angel θ = 0 Resultant intensity at the third vertex = + = + + cosφ = + + = watt/m 9. For the study of the helical structure of nucleic acids, the property of electromagnetic radiation, generally used is [EAMCET 005 M] ) Reflection ) nterference 3) Diffraction ) Polarization Ans: By using the property of polarisation helical structure of nucleic acids can e studied. 0. Assertion (A) : n Young s interference experiment the incident light used is white. When one slit is covered with red filter and the other with a lue filter, the phase difference at any point on the screen will continuously change producing uniform illumination. Reason (R ) : Two independent source of light would no longer act as coherent sources. [EAMCET 00 M ] ) Both A and R are true and R is the correct explanation of A ) Both A and R are true and R is not the correct explanation of A 3) A is true ut R is false ) A is false ut R is true Ans: The condition for interference is that two independent sources of light cannot act as coherent sources. Both A and R are true and R is the correct explanation of A. Consider the following statement A and B and identify the correct answer: [EAMCET 003 M] A : Polarized light can e used to study the helical structure of nucleic acids B: Optic axis is a direction and not any particular line in the crystal ) A and B are correct ) A and B are wrong 3) A is correct and B is wrong ) A is wrong and B is correct Ans:

6 Both A and B are correct statements. When two coherent monochromatic light eams of intensities and aer super imposed, the ratio etween maximum and minimum intensities in the resultant eam is [EAMCET 00 M] ) 9 : ) : 9 3) : ) : Ans: max + = min + 9 = = = 9 3. Consider the following two statements A and B and identify correct choice in the given answer. A: When the light falls in two Polaroid sheets having their axis mutually perpendicular, it is completely extinguished. B : When poly vinyl alcohol is sujected to a large strain the molecules get oriented parallel to the direction of strain and material ecomes doule refractive. [EAMCET 00 M] ) A and B are correct ) Both A and B are wrong 3) A correct B wrong ) A wrong B correct Ans: 0 From the relation = cos θ, when θ= 90, = 0 Both A and B are correct. A wavefront is an imaginary surface where [EAMCET 00 M] ) Phase is same for all points ) Phase changes at constant rate at all points along the surface 3) Constant phase difference continuously changes etween the points ) Phase changes all over the surface Ans: Wave front is an imaginary surface where the phase is same for all points. 5. Both light and sound waves produce diffraction. t is more difficult to oserve diffraction with light waves ecause [EAMCET 00 M] ) Light waves do not require medium ) Wavelength of light waves is far smaller 3) Light waves are transverse waves ) Speed of light is far greater Ans: As the wavelength of light waves is very les it is difficult to oserve diffraction with light waves. 6

Optics. n n. sin c. sin

Optics. n n. sin c. sin Optics Geometrical optics (model) Light-ray: extremely thin parallel light beam Using this model, the explanation of several optical phenomena can be given as the solution of simple geometric problems.