Previous Years Questions of Physics of AHSEC class 12 : Unit 10 – Wave Optics
1-Mark Questions (Section -VSA :- Very Short Answer)
01:- What is the shape of the wavefront diverging from a point source? (2026)
02:- State one difference between interference and diffraction. (2025)
03:- What is the shape of the wavefront of light emitted by a long neon bulb placed at a finite distance ? (2015)
03:- 2-Mark Questions (Section -SA :- Short Answer)
01:- Monochromatic light of wavelength 589 nm is incident from air on a water surface. Calculate the wavelength and frequency of (i) reflected and (i) refracted light.The refractive index of water is μ =1. 33. ½×4=2 (2026)
02:- Draw diagrams to show the refraction of a plane wave by (i) a thin prism, (i) a convex lens. 1+1=2 (2026)
03:-If 1 and 2 be the denser (water) and rarer (air) media respectively and iC be the critical angle, what will be the expressions for n12 and n21 ? (2024)
04:- A plane wavefront is travelling from lighter medium 1 to denser meat 2 through the interface of mediums 1 and 2 with velocities v1 and v2 and you know well that sin i/ sin r = v1 / v2, where i and r are the angles of incidence and refraction. If 1y and n, be the refractive indices of the mediums thèn derive Snell’s law. (2023)
05:- Two slits are 1mm apart and a screen is placed at some distance When the slits are illuminated with light of wavelength 500nm, fringe separation obtained on the screen is 0.5mm. What is the distance between the screen and the slits ? 2 (2018)
06:- State two important differences between interference and diffraction. (2014)
3-Mark Questions (Section -LA :- Long Answer)
01: Under what condition, two sources are said to be coherent? Waves of wavelength λ coming from two coherent sources S1 and S2 meet at a point P. If S1P ~ S2P = △, write the conditions for (i) constructive interference and (ii) destructive interference at P. 1+1+1=3
(2026)
02:- In a Young’s double slit experiment, light of wavelength 500 nm is incident on two slits, which are 1 mm apart. If the screen is placed at a distance of 1 m from the slits, calculate the fringe width of the fringe pattern. When the double slit in Young’s experiment is replaced by a single slit, name the pattern of fringes formed on the screen. 2+1=3 (2026).
03:-State Huygens principle and define wavefront. To represent a wavefront draw a semicircular line of a suitable radius. Now draw the next forwarding wavefront by drawing a few secondary wavelets after the time τ. The speed of the wave is v. 1½+½+1=3. (2025).
04:- In a Young’s double-slit experiment, monochromatic light of wavelength 600 nm is used. Determine the distance of the screen from the slits if the slits are separated by 0.28 mm and the distance of the central bright fringe and the fourth bright fringe is 1.2 cm. 3 (2025)
05:-Discuss the phenomenon of refraction of a plane wave at a denser medium and show that in this phenomenon frequency remains the same. 2+1=3 (2024)
06:- In Young’s double-slit experiment, the slits are separated by 2.8×104m and the screen is placed 1.4m away. The distance between the central bright fringe and the fourth bright fringe is 1.2×10-2m. Determine the wavelength of light used in the experiment in nm.(2024)
07:- State superposition principle of waves. Mention at least one example of coherent source of light. What will be the phase difference between two light waves, if the path difference between them is 2.5λ ? 1+½+1½=3 (2022)
08:- Find out an expression for fringe width in Young’s double slit experiment. Light of wavelength 500 nm is incident on two slits which are 1mm apart. If the screen is placed at a distance of 1 m from the slits, calculate the fringe width of the fringe pattern formed on the screen. 3+2=5. (2022)
09:- What are coherent sources? In a Young’s double slit experiment the intensity of light at a point on the screen where path difference is k units. Find the intensity at a point where the path difference is λ/3 . 1+2=3 (2019)
10:– Deduce Snell’s Law of refraction for a plane wave using Huygens’ principle. (2018)
11:- The equations of light wave from two sources are y1 = a1 sinϖt and y2 = a2 sin(ϖt +ф) where the symbols have their usual meaning. The individual intensities are I1 and I2. Show that the minimum resultant intensity due to superposition is 
(2017)
12:- What is a Coherent Source ? State two differences between interference and diffraction. 1+2=3. (2015)
13:- Find the expression of fringe 
width for Young’s double slit interference pattern where 2d is the separation between the two coherent sources. 3. (2014)
5-Mark Questions (Section -LA :- Long Answer)
01:- Using Huygens’ principle, discuss either the phenomenon of reflection or the phenomenon of refraction. 5. (2026)
02:– Discuss the diffraction of light due to single slit. (2025)
03:- Discuss the phenomena of diffraction produced by a single slit by drawing a neat diagram. 1+4=5. (2023)
04:- When the double slit in Young’s experiment is replaced by a single slit, name the pattern of fringes formed on the screen. What is the phenomenon due to which we see colours when a CD is viewed ? Mention at least one difference in the fringe pattern observed due to interference and diffraction phenomena. Describe a simple experiment by which you can observe the diffraction phenomenon in your home. 1+1+1+2=5 (2022)
05:- State Huygens’ principle in optics. Using this principle derive the law of reflection or refraction. Which quantity remains unchanged when a light wave suffers reflection or refraction ? 1+3+1=5. (2020)
06:- With the help of Young’s double-slit arrangement to produce interference pattern, derive an expression for fringe width β . Mention at least one difference between the interference fringes and diffraction fringes. Are two identical bulbs of same power and manufactured by the same company coherent sources ? 4+½+½=5. (2020)
07:- Answer any two of the following : 2X2½=5. (2018)
(i ) “When monochromatic light is incident on a surface separating two media, the reflected and refracted light both have same frequency as the incident frequency”. Is this statement true? If yes, why? If you think it is not true, why?
(ii) What is the effect on the interference fringes in Young’s double slit experiment when the monochromatic source is replaced by a source of white light?
(iii) “In between a fixed object and a fixed screen, a convex lens can cast two images at two different positions of the lens.” Taking this to be a true statement show that product of the image sizes is equal to the square of the object size.
(iv) If you move the source slit closer to the double slit in Young’s experiment, what will be effect on the fringes?
08:- A beam of light consisting of wavelengths 6500Å and 5200Å is used in Young’s double slit experiment of slit separation 2mm and where the screen is 120cm away. Find the distance to the third fringe from the central maximum for the wavelength 6500Å. What is the least distance from the central maximum at which the bright fringes due to both wavelengths coincide ? 1+4=5. (2016)
09:- Explain Huygen’s principle of wave optics. Use this principle to prove the laws of retraction in case of a plane surface. (2015)
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