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question_answer1) What are the reasons to believe that light is a wave motion?
question_answer2) How much is the phase difference corresponding to path difference of \[\lambda \] of two waves reaching a point?
question_answer3) A and B are two points on a water surface where waves are generated. What is the phase difference if (a) A and B are on the same wavefront but separated in distance by the wavelength \[\lambda \]. (b) If A and B are on successive crests, but linearly separated by the distance \[2.5\lambda \] and (c) A and B are on successive troughs?
question_answer4) Is it necessary that the amplitude be constant over a given wave front?
question_answer5) Can two wave-fronts cross one another? Give reason.
question_answer6) A light wave enters from air into glass. How will the following be affected: (i) Energy of the wave (ii) Frequency of the wave?
question_answer7) When a wave undergoes reflection at a denser medium, what happens to its phase?
question_answer8) If a wave undergoes refraction, what will be the phase change?
question_answer9) When monochromatic light travels from one medium to another its wavelength changes but frequency remains the same. Explain.
question_answer10) Define the term 'coherence' for light waves.
question_answer11) State the essential conditions for two light waves to be coherent.
question_answer12) State two conditions to obtain sustained interference of light.
question_answer13) What happens to the interference pattern if the phase difference between the two sources varies continuously?
question_answer14) Why are coherent sources necessary to produce a sustained interference pattern?
question_answer15) Two slits in Young's double slit experiment are illuminated by two different lamps emitting light of the same wavelength. Will you observe the interference pattern? Justify your answer.
question_answer16) Two independent light sources cannot act as coherent sources'. Why?
question_answer17) A slit, S is illuminated by a monochromatic source of light to give two coherent sources \[{{P}_{1}}\] and \[{{P}_{2}}\]. These give bright and dark bands on a screen. At a point R, on the screen, there is a dark fringe. What relationship must exist between the lengths \[{{P}_{1}}R\] and\[{{P}_{2}}R\]?
question_answer18) If the separation between the two slits is decreased in Young's double slit experiment keeping the screen position fixed, what will happen to the fringes width?
question_answer19) How does the fringe width, in Young's double-slit experiment, change when the distance of separation between the slits and screen is doubled?
question_answer20) Why should we have a narrow source to produce good interference fringes?
question_answer21) In Young's double slit experiment if the distance between two slits is halved and distance between the slits and the screen is doubled, then what will be the effect on fringe width?
question_answer22) No interference pattern is detected when two coherent sources are infinitely close to one another. Why?
question_answer23) Why is interference pattern not detected when the two coherent sources are far apart?
question_answer24) If the path difference produced due to interference of light coming out of two slits for yellow colour of light at a point on the screen be \[3\lambda /2\],will be the colour of the fringe at the point ? Give reason also.
question_answer25) Two identical coherent waves, each of intensity \[{{I}_{0}}\], are producing an interference pattern. Write the value of the resultant intensity at a point of (i) constructive interference and (ii) destructive interference.
question_answer26) In Young's double slit experiment lights of green, yellow and orange colours are successively used. Write the fringe widths for the three colour in increasing order.
question_answer27) When a thin transparent film is Placed just in front of one of the slits in the Young's double slit experiment using white light, what change results in the fringe system?
question_answer28) How will the intensity of maxima and minima, in the Young's double slit experiment change, if one of the two slits is covered by a transparent paper which transmits only half of the light intensity?
question_answer29) State with reason whether diffraction of light takes place at the two slits in the Young's interference experiment.
question_answer30) Explain the statement 'light added to light can produce darkness'.
question_answer31) What happens to the light energy when light waves interfere destructively at a point?
question_answer32) What will be the effect on the fringes formed in Young's double slit experiment, if the apparatus is immersed in water?
question_answer33) Why is it comparatively difficult to observe interference in light waves as compared to that in water waves?
question_answer34) Is there any difference between the colours emerging from a prism and the colours of a soap film seen in sunlight?
question_answer35) Why does a soap bubble show beautiful colours when illuminated by white light?
question_answer36) Why does an excessively thin film appear black in reflected light?
question_answer37) Why do thick films not show interference effects?
question_answer38) The central fringe obtained with a Lloyd's mirror set up for interference is found to be dark, whereas it is bright with a biprism. Why?
question_answer39) State the essential condition for diffraction of light to occur.
question_answer40) What should be the order of size of obstacle or aperture for diffraction of light?
question_answer41) How does the angular separation between fringes in single-slit diffraction experiment change when the distance of separation between the slit and screen is doubled?
question_answer42) Why does the intensity of the secondary maximum become less as compared to the central maximum?
question_answer43) Yellow light is used in a single slit diffraction experiment with slit width of 0.6 mm. If yellow light is replaced by X-rays, how will the diffraction pattern be affected?
question_answer44) Is it correct to say that diffraction is interference between different parts of the same wavefront?
question_answer45) What is the basic difference between interference and diffraction of light?
question_answer46) A small circular disc is placed in the path of light from a distant source. Will the centre of shadow be bright or dark?
question_answer47) Why do we fail to observe the diffraction from a wide slit illuminated by monochromatic light?
question_answer48) Diffraction is common in sound but not common in light waves? Why? Or Why do we not encounter diffraction effects of light in everyday observations?
question_answer49) Radio waves diffract pronouncedly around the buildings, while light waves, which are e. m. waves, do not. Why?
question_answer50) If light bends around obstacles, then why can't we see around a building?
question_answer51) You are able to hear a person standing behind a wall but not see him, though both light and sound are waves. Why?
question_answer52) A single slit diffraction pattern is completely immersed in water without changing any other parameter. How is the width of central maximum affected?
question_answer53) Coloured spectrum is seen, when we look through a muslin cloth. Why?
question_answer54) Why are diffraction effects more prominent through a slit formed by two blades than through a slit formed by two fingers?
question_answer55) How does the resolving power of a telescope change when the aperture of the objective is increased?
question_answer56) What is the relation between magnifying power and resolving power of a telescope?
question_answer57) Why is the resolving power of a microscope having oil immersion objective high?
question_answer58) Which type of waves show the property of polarisation?
question_answer59) Which special characteristic of light is demonstrated only by the phenomenon of polarisation?
question_answer60) Will ultrasonic waves show any polarisation? Give reasons for your answer.
question_answer61) Why longitudinal waves cannot be polarised?
question_answer62) Light waves can be polarised while sound waves cannot. Why?
question_answer63) Which plane is defined as the plane of polarization in a plane polarized electromagnetic wave?
question_answer64) Name three properties, which are mutually perpendicular to each other in a plane, q polarized light wave.
question_answer65) Which field vector, electric or magnetic, is used to represent the polarisation of an e. m. wave?
question_answer66) Why does the electric field of e. m. wave determine the state of polarisation and not its magnetic field?
question_answer67) Does the value of polarising angle of incidence depend on the colour of light?
question_answer68) If the polarizing angle for air-glass inter- face is\[\mathbf{56}.\mathbf{3}{}^\circ \], what is the angle of refraction in glass?
question_answer69) At what angle of incidence should a light beam strike a glass slab of refractive index \[\sqrt{3}\], such that the reflected and the refracted rays are perpendicular to each other? Or What is the polarising angle of a medium of refractive index \[\sqrt{3}\]\[(\mathbf{or}\text{ }\mathbf{1}.\mathbf{732}\])?
question_answer70) Sun glasses are made of polaroids and not of coloured glasses. Why?
question_answer71) Write two simple uses of polaroids.
question_answer72) A partially plane polarised beam of light is passed through a polaroid. Show graphically the variation of the transmitted light intensity with angle of rotation of the polaroid.
question_answer73) Compare Maxwell's electromagnetic theory with Huygens' theory of light.
question_answer74) Answer the following questions : (a) When monochromatic light is incident on a surface separating two media, the reflected and refracted light both have the same frequency as the incident frequency. Explain why. (b) When light travels from a rarer to a denser medium, it loses some speed. Does the reduction in speed imply a reduction in the energy carried by the light wave? (c) A narrow pulse of light is sent through a medium. Will you expect the pulse to retain its shape as it travels through the medium? (d) In the wave picture of light, intensity of light is determined by the square of the amplitude of the wave. What determines the intensity of light in the photon picture of light? (e) The speed of light in still water is \[c/\mu \]where \[\mu \], is the refractive index of the water. What is the speed of light in a stream of water flowing at a steady speed of \[\upsilon \]relative to the observer?
question_answer75) If \[{{\varepsilon }_{0}}\] and \[{{\mu }_{0}}\] are the permittivity and permeability of free space and \[\varepsilon \] and \[\mu \] are corresponding quantities for a medium, then show that the refractive index of the medium is \[\sqrt{\frac{\mu \varepsilon }{\mu {{\varepsilon }_{0}}}}\].
question_answer76) How is a wavefront different from a ray? Draw the geometrical shape of the wavefronts when (i) light diverges from a point source, and (ii) light emerges out of convex lens when a point source is placed at its focus.
question_answer77) (a) A plane wavetront approaches a plane surface separating two media. If medium one is (optically) denser and medium two is (optically) rarer, construct the refracted wave front using Huygens' principle. Hence prove Snell?s law. (b) Draw the shape of the refracted/reflected wavefront when a plane wavefront is incident on (i) prism and (ii) convex mirror. Give a brief explanation for the construction.
question_answer78) A region is illuminated by two sources of light. The intensity \[I\] at each point is found to be equal to \[{{I}_{1}}+{{I}_{2}}\], where \[{{I}_{1}}\] is the intensity of light at the point when source 2 is absent. \[{{I}_{1}}\] is similarly defined. Are the sources coherent or incoherent? Explain.
question_answer79) What is the effect on the interference fringes in a Young's double-slit experiment due to each of the following operations : (a) The screen is moved away from the plane of the slits. (b) The (monochromatic) source is replaced by another (monochromatic) source of shorter wavelength. (c) The separation between the two slits is increased. (d) The source slit is moved closer to the double-slit plane. (e) The width of the source slit is increased. (f) The widths of two slits are increased. (g) The monochromatic source is replaced by source of white light? (In each operation, take all parameters, other than the one specified, to remain unchanged.)
question_answer80) What is meant by coherent sources of light? Can two identical and independent sodium lamps act as coherent sources? Give reason for your answer.
question_answer81) What will be the effect on the interference fringes in Young's double slit experiment when, (i) the monochromatic source is replaced by another monochromatic source of shorter wavelength? (ii) monochromatic source is replaced by a source of white light. Justify your answer in each case?
question_answer82) What is the effect on the interference pattern observed in a Young's double slit experiment in the following cases: (i) Screen is moved away from the plane of the slits. (ii) Separation between the slits is increased. (ii) Widths of the slits are doubled.
question_answer83) What is the effect on the interference fringes in Young's double slit experiment if (i) the separation between the slits is halved, and (ii) the source slit is moved closer to the double slit? Justify your answer.
question_answer84) Why is no interference pattern observed when two coherent sources are (i) infinitely close to each other? (ii) far apart from each other?
question_answer85) What changes in the interference pattern in Young's double slit experiment will be observed when (i) light of smaller frequency is used? (ii) the apparatus is immersed in water?
question_answer86) In a Young's double slit experiment, the position of the first fringe coincides with \[{{S}_{1}}\] and \[{{S}_{2}}\] respectively. What is the wavelength of light?
question_answer87) One of the two slits in Young's double slit experiment is so painted that it transmits half the intensity of the other. What is the effect on interference fringes?
question_answer88) Two sources of intensity \[{{I}_{1}}\] and \[{{I}_{2}}\] undergo interference in Young's double slit experiment. Show that \[\frac{{{I}_{\max }}}{{{I}_{\min }}}={{\left( \frac{{{a}_{1}}+{{a}_{2}}}{{{a}_{1}}-{{a}_{2}}} \right)}^{2}}\], where \[{{a}_{1}}\] and \[{{a}_{2}}\] are the amplitudes of disturbance for two sources \[{{S}_{1}}\], and \[{{S}_{2}}\].
question_answer89) In Fig. two light waves of the same frequency start from the sources \[{{S}_{1}}\] and \[{{S}_{2}}\] in the same phase. The distance \[{{S}_{1}}{{S}_{2}}=\lambda /2\]. What will be the nature of the interference at the points A, B and C?
question_answer90) Interference can be observed with two independent tuning forks but it cannot be observed with two independent bulbs. Why?
question_answer91) Two narrow slits are illuminated by a single monochromatic source. Name the pattern obtained on the screen. One of the slits is now completely covered. What is the name of the pattern now obtained on the screen? Draw intensity pattern obtained in the two cases. Also write two differences between the patterns obtained in the above two cases.
question_answer92) What change will occur in diffraction pattern if (i) light of smaller wavelength is used (ii) slit is made narrower, and (iii) another slit is placed near and parallel to the first slit?
question_answer93) Draw the diagram showing intensity distribution of light on the screen for diffraction of light at a single slit. How is the width of central maxima affected if (i) the width of the slit is doubled; (ii) the wavelength of the light used is increased? What happens to the width of the central maxima if the whole apparatus is immersed in water and why?
question_answer94) State with reason, how would the linear width of central maximum change if (i) monochromatic yellow light is replaced with red light, and (ii) distance between the slit and the screen is increased.
question_answer95) In a single slit diffraction pattern, how does the angular width of central maximum change, when (i) slit width is decreased, (ii) distance between the slit and screen is increased and (iii) light of smaller visible wavelength is used? Justify your answer in each case.
question_answer96) State the condition for diffraction of light to occur. In the diffraction at a single slit experiment, how would the width and the intensity of central maximum change, if (i) slit width is halved and (ii) visible light of longer wavelength is used?
question_answer97) In a single slit diffraction experiment, the slit width is made double that of the original width. What would happen to the size and intensity of central diffraction band? Give reason for your answer.
question_answer98) What two main changes in diffraction pattern of single slit will you observe when the mono-chromatic source of light is replaced by a source of white light ?
question_answer99) Give reasons for the following : (i) Astronomers prefer to use telescopes with large objective diameters to observe astronomical objects. (ii) Two identical but independent monochromatic sources of light cannot be coherent. (iii) The value of the Brewster angle for a trans- parent medium is different for lights of different colours.
question_answer100) How will the angular separation and visibility of fringes in Young's double slit experiment change when (i) screen is moved away from the plane of the slits, and (ii) width of the source slit is increased?
question_answer101) Distinguish between magnifying power and resolving power of a microscope.
question_answer102) Define the terms magnifying power and solving power of a telescope.
question_answer103) How does the resolving power of a compound microscope change, when (i) refractive index of the medium between the object and the objective lens increases ; and (ii) wavelength of the radiation used is increased ?
question_answer104) Explain with reason, how the resolving power of a compound microscope will change when (i) frequency of the incident light on the objective lens is increased, (ii) focal length of the objective lens is increased, and (iii) aperture of the objective lens is increased.
question_answer105) How does the resolving power of a compound microscope change on (i) decreasing the wavelength of light used, and (ii) decreasing the diameter of its objective lens?
question_answer106) How does the resolving power of a telescope change if (i) the size of the aperture of the objective lens is increased, (ii) the focal length of the objective lens is decreased ?
question_answer107) Explain with reason, how the resolving power of an astronomical telescope will change when (i) frequency of the incident light on the objective lens is increased, (ii) focal length of the objective lens is increased, and (Hi) aperture of the objective lens is halved.
question_answer108) On what factors, does the (i) magnifying power and (ii) resolving power of a compound microscope depend?
question_answer109) On what factors, does the (i) magnifying power and (ii) resolving power of a refracting type astronomical telescope depend?
question_answer110) How does the (i) magnifying power and (ii) resolving power of a telescope change on increasing the diameter of its objective? Give reasons for your answer.
question_answer111) Which of the following waves can be polarised: (i) X-rays, (ii) sound waves? Give reasons.
question_answer112) What is a polaroid? How is plane polarised light obtained with its help? How will you use it to distinguish between unpolarised light and plane polarised light?
question_answer113) When a sheet of transparent plastic is placed between two crossed polarizers, no light is transmitted. When the sheet is stretched in one direction, some light passes through the crossed polarizers. What is happening?
question_answer114) Show that when a ray of light is incident on the surface of a transparent medium at the polarizing angle, the reflected and transmitted rays are perpendicular to each other.
question_answer115) The critical angle between a given transparent medium and air is denoted by \[{{i}_{c}}\]. A ray of light in air medium enters this transparent medium at an angle of incidence equal to the polarizing angle \[({{i}_{p}}).\] Deduce a relation for the angle of refraction \[({{r}_{p}})\] in terms of \[{{i}_{c}}\].
question_answer116) Define critical angle and polarising angle. What is the relation between the two angles?
question_answer117) Green light is incident at the polarizing angle on a certain glass plate. The angle of refraction is\[\mathbf{32}{}^\circ \]. What are : (i) the polarizing angle, (ii) the index of refraction of glass? (iii) Indicate the polarisation components (of electric field) on the reflected and refracted rays, by double arrows and dots.
question_answer118) Define Brewster angle. Show that the Brewster angle \['{{i}_{B}}'\] for a given pair of transparent media, is related to the critical angle \[{{i}_{e}}\] through the relation, \[{{i}_{c}}={{\sin }^{-1}}\]\[(\cot {{i}_{B}})\].
question_answer119) A light beam is incident on the boundary between two transparent media. At a particular angle of incidence the reflected ray is perpendicular to the refracted ray. Obtain an expression for this angle of incidence. Does this angle depend on the wavelength of light used?
question_answer120) Give reasons for the following : (a) Astronomers prefer to use telescopes with large objective diameters to observe astronomies objects. (b) Two identical but independent monochromatic sources of light cannot be coherent. (c) The value of the Brewster angle for a transparent medium is different for lights of different colours.
question_answer121) Give reason for each of the following observations : (i) The resultant intensity at any point on the screen varies between zero and four times the intensity due to one slit, in young's double slit experiment. (ii) A few coloured fringes, around a central white region, are observed on the screen, when the source of monochromatic light is replaced by white light in Young's double slit experiment. (iii) The intensity of light transmitted by a polariod is half the intensity of the light incident on it.
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