WAVE OPTICS
SL. NO. / QUESTION / M.M. / YEAR1 / What is the geometrical shape of the wavefront when a plane wave passes through a convex lens? / 1 / 2008
2 / How wouldthe angular separation of interference fringes in Young’s double slit experiment change when the distance between the slits and screen is doubled? / 1 / 2009
3 / How does the fringe width, in Young’s double-slit experiment, change when the distance of separation between the slits and screen is doubled? / 1 / 2012
4 / Compare and contrast the pattern which is seen with two coherently, illuminated narrow slits in Young’s experiment with that seen from coherently illuminated single slit producing diffraction. / 2 / 2006
5 / Define the term ‘linearly polarised light’.
When does the intensity of transmitted light become maximum, when a Polaroid sheet is rotated between two crossed Polaroids? / 2 / 2009
6 / A beam of light consisting of two wavelengths, 800 nm and 600 nm is used to obtain the interference fringes in a Young’s double slit experiment on a screen placed 1.4 m away. If the two slits are separated by 0.28 mm, calculate the least distance from the central bright maximum where the bright fringes of the two wavelengths coincide. / 2 / 2012
7 / Two wavelengths of sodium light 590 nm and 596 nm are used, in turn, to study the diffraction taking place at a single slit of aperture 2 x 10-4 m. The distance between the slit and the screen is 1.5 m. Calculate the separation between the positions of the first maxima of the diffraction pattern obtained in the two cases. / 2 / 2013
8 / State clearly how an unpolarised light gets linearly polarised when passed through a Polaroid.
a) Unpolarised light of intensity Io is incident on Polaroid P1 which is kept near another Polaroid P2 whose pass axis is parallel to that of P1. How will the intensities I1 and I2, transmitted by the Polaroids P1 and P2 respectively change on rotating P1 without disturbing P2?
b) Write the relation between the intensities I1 and I2. / 3 / 2015
9 / Use Huygens` principle to show how a plane wave front propagates from a denser to rarer medium. Hence verify snell`s law of refraction. / 3 / 2015
10 / Answer the following :
(a)When a tiny circular obstacle is placed in the path of light from a distance source, a bright spot is seen at the centre of the shadow of the obstacle. Explain, why?
(b)How does the resolving power of a microscope depend on (i) the wave length of the light used and (ii) the medium between the object and the objective lens? / 2 / 2015
11 / In Young’s doubled slit experiment , monochromatic light of wavelength 630 nm illuminates the pair of slits and produces an interference pattern in which two consecutive bright fringes are separated by 8.1 nm. another source of monochromatic light produces the interference pattern in which the two consecutive bright fringes are separated by 7.2 nm . Find the wave length of light from the second source.
What is the effect on the interference fringes if the monochromatic source is replaced by a source of white light? / 3 / 2009
12 / How does an unpolarised light get polarized when passed through polaroid?
Two polaroids are set in crossed positions. A third polaroid is placed between the two making an angle ? with the pass axis of the first polaroid. Write the expression of the intensity of light transmitted from the second polaroid. In what orientations will the transmitted intensity be (i) minimum and (ii) maximum? / 3 / 2010
13 / (a)State Huygens` principle. Using this principle explain how a diffraction pattern is obtained on a screen due to a narrow slit on which a narrow beam coming from a monochromatic source of light is incident normally.
(b)Show that the angular width of the first diffraction fringe is half of that of the central fringe.
(c)If a monochromatic source of light is replaced by white light, what change would you observe in the diffraction pattern? / 3 / 2011
14 / (a) Using the phenomenon of polarisation, show how transverse nature of light can be demonstrated.
(b)Two polaroids P1 and P2are placed with their pass axes perpendicular to each other. Unpolarised light of intensity I0is incident on P1 .A third polaroid P3is kept in between P1and P2 such that its pass axis makes an angle of 300 with that of P1. Determine the intensity of light transmitted through P1,P2and P3. / 3 / 2014
15 / (a) The light from a clear blue portion of the sky shows a rise and fall of intensity when viewed through a Polaroid which is rotated. Describe, with the help of a suitable diagram, the basic phenomenon/process which occurs to explain this observation.
(b) Show how light reflected from a transparent medium gets polarized. Hence deduce Brewster’s law / 3 / 2015
16 / (a) Define a wave front.
(b) Using Huygens` principle, draw diagrams to show the nature of the wave fronts when an incident plane wave front gets
(i) reflected from a concave mirror,
(ii) refracted from a convex lens. / 3 / 2015
17 / What are coherent sources? Why are coherent sources required to produce interference of light? Give an example of the interference of light in everyday life.
In Young’s double slit experiment, the two slits are 0.03 cm apart and the screen is placed at a distance of 1.5 m away from the slits. The distance between the central bright fringe and fourth bright fringe is 1 cm. Calculate the wavelength of light used. / 5 / 2007
18 / State the condition under which the phenomenon of diffraction of light takes place. Derive the expression for the width of the central maximum due to diffraction of light at a single slit.
A slit if width ‘a’ is illuminated by a monochromatic light of wavelength 700 nm at normal incidence. Calculate the value of ‘a’ for position of
(i)First minimum at an angle of diffraction of 30o.
(ii)First maximum at an angle of diffraction of 30o. / 5 / 2007
19 / (a) In a single slit diffraction experiment, a slit of which ‘d’ is illuminated by red light of wavelength 650 nm. For what value of ‘d’ will:
(i)The first minimum fall at an angle diffraction of 30o, and
(ii)The first maximum fall at an angle of diffraction 30o?
(b)Why does the intensity of the secondary maximum become less as compared to the central maximum? / 5 / 2009
20 / In Young’s double slit experiment, the two slits 0.15 mm apart are illuminated by monochromatic light of wavelength 450 nm. The screen is 0.1 m away from the slits.
(a)Find the distance of the second (i) bright fringe, (ii) dark fringe from the central maximum.
(b)How will the fringe pattern change if the screen is moved away from the slits? / 5 / 2010
21 / State the importance of coherent sources in the phenomenon of interference.
In Young’s double slit experiment to produce interference pattern, obtain the conditions for constructive and destructive interference. Hence deduced the expression for the fringe width. How does the fringe width get affected, if the entire experimental apparatus of Young is immersed in water? / 5 / 2011
22 /
- How does an unpolarised light incident on a polaroid get polarised?
- Two polaroids ‘A’ and ‘B’ are kept in crossed position. How should a third Polaroid ‘C’ be placed between them so that the intensity of polarised light transmitted by Polaroid ‘B’ reduces to 1/8th of the intensity of unpolarised light incident on A?
23 / (a) In Young’s double slit experiment, describe briefly how bright and dark fringes are obtained on the screen kept in front of a double slit. Hence obtain the expression for the fringe width.
(b) The ratio of the intensities at minima to the maxima in the Young’s double slit experiment is 9:25. Find the ratio of the widths of the two slits. / 5 / 2014
24 / (a)Describe briefly how a diffraction pattern is obtained on a screen due to a single narrow slit illuminated by a mono-chromatic source of light. Hence obtain the conditions for the angular width of secondary minima.
(b)Two wave lengths of sodium light of 590 nm and 596 nm are used in turn to study the diffraction taking place at a single slit of aperture 2x 10-6 m. The distance between the slit and the screen is 1.5 m. Calculate the separation between positions of first maxima of the diffraction pattern obtained in the two cases. / 5 / 2014
25 / Consider two coherent sources S1 and S2 producing monochromatic waves to produce interference pattern. Let the displacement of the wave produced by S1 be given by Y1 = a cosωtand the displacement by S2 be Y2 = a cos (ωt+ϕ).
Find out the expression for the amplitude of the resultant displacement at a point and show that intensity at that point will be
I =4a2cos2ϕ/2.
Hence establish the condition for constructive and destructive interference.
What is the effect on the interference fringes in Young’s double slit experiment when (i) the width of the slit is increased ; (ii) the monochromatic source of light is replaced by a source of white light? / 5 / 2015
26 / (a) Using Huygens` construction of secondary wavelets explain how a diffraction pattern is obtained on a screen due to a narrow slit on which a narrow beam coming from a monochromatic source of light is incident normally.
(b)Show that the angular width of the first diffraction fringe is half of that of the central fringe.
(c)Explain why the maxima at becomes weaker and weaker with increasing n. / 5 / 2015