Wave Optics: Class 12 Previous Year Questions

Wave Optics questions asked in CBSE board exams

Repeated questions first. Open the free app to see each question as it appeared in the paper, with its marking scheme.

1. (a) A beam of light consisting of two wavelengths 400 nm and 600 nm is used to illuminate a single slit of width 1 mm. Find the least distance of the point from the central maximum where the dark fringes due to both wavelengths coincide on the screen placed 1.…
   Board 20262 marksshort answer
2. A 5 cm long pencil is placed along the principal axis of a concave mirror of focal length 20 cm such that its nearest end is at a distance of 25 cm from the mirror. Calculate the length of the image of the pencil. 2 OR In a Young’s double-slit experiment, a be…
   Board 20262 marksshort answer
3. The shape of the interference fringes in Young’s double-slit experiment, when the distance between the slit and the screen is very large as compared to the slit-separation, is nearly 1 (A) straight (B) parabolic (C) circular (D) hyperbolic
   Board 20261 markMCQ
4. SECTION – E 31. (a) What are coherent sources ? Why they are necessary for observing stable interference pattern ? Draw a graph showing the variation of intensity of light with the position on the screen in Young’s double- slit experiment. 5 (b) Find the inten…
   Board 20265 markscase-based
5. Four independent waves are expressed as 1 (i) y1 = A1 sin t (ii) y2 = A2 sin 2 t (iii) y3 = A3 cos t (iv) y4 = A4 sin (t + /3) The interference between two of these waves is possible in (A) (i) and (iii) only (B) (iii) and (iv) only (C) (i), (iii) and (iv…
   Board 20261 markMCQ
6. ( ) p y g p 14. Assertion (A) : If accelerated electrons are passed through a narrow slit, a diffraction pattern is observed. 1 Reason (R) : Electrons behave as both particles and waves.
   Board 20261 markAssertion-Reason
7. Assertion (A) : Light added to light can produce darkness. 1 Reason (R) : When two coherent light waves interfere, there is darkness at position of destructive interference.
   Board 20261 markAssertion-Reason
8. (a) In a diffraction experiment, the slit is illuminated by light of wavelength 600 nm. The first minimum of the pattern falls at = 30°.Calculate the width of the slit. OR (b) In a Young's double-slit experiment, two light waves, each of on the screen. Find th…
   Board 20252 marksshort answer
9. (i) (1) (a) What are coherent sources ? Why are they necessary for observing a sustained interference pattern ? (2) Lights from two independent sources are not coherent. Explain. (i) Two slits 0.1 mm apart are arranged 1.20 m from a screen. Light of wavelength…
   Board 20255 markscase-based
10. (i) (a) A thin pencil of length (f/4) is placed coinciding with the principal axis of a mirror of focal length f. The image of the pencil is real and enlarged, just touches the pencil. Calculate the magnification produced by the mirror. (ii) A ray of light is …
    Board 20255 markslong answer
11. In a double-slit experiment, 6th dark fringe is observed at a certain point of the screen. A transparent sheet of thickness t and refractive index n is now introduced in the path of one of the two interfering waves to increase its phase by 2· (n - 1) t/2. The …
    Board 20252 marksshort answer
12. AmaoI _| VrZ AmXe© ~¡Q>[a`m| Ho$ gmW {dÚwV n[anW Xem©`m J`m h¡ & BgH$s emImAm| AG, BF Am¡a CD _| {dÚwV YmamAm| Ho$ n[a_mU Am¡a {XemE± kmV H$s{OE & 3 18. (a) two coherent sources of light superpose at a point. If the phase difference between the two waves is , …
    Board 20243 marksshort answer
13. Assertion (A) : In Young's double slit experiment all fringes are of equal width. Reason (R) : The fringe width depends upon wavelength of light (2) used, distance of screen from plane of slits (D) and slits separation (d).
    Board 20231 markAssertion-Reason
14. (H$) (i) (1) ì`{VH$aU n¡Q>Z© Am¡a {ddV©Z n¡Q>Z© Ho$ ~rM Xmo AÝVa {b{IE & (2) `§J Ho$ {Û{Par à`moJ _| {H$Ýht Xmo H$maH$m| Ho$ Zm_ {b{IE {OZ na q\ 32. (a) (i) State Biot- carrying element. Use this law to obtain an expression for the current loop indicating the …
    Board 20235 markslong answer
15. What happens to the interference pattern when two coherent sources are (a) infinitely close, and (b) far apart from each other Page 11 of 24 23. 1 h · h ·he (a) 24. T0 1 25. : (i) 26.a (b) a C f - (A) f a V a (i) (ii) :A B f Af 27 28. CR R = 200 C =(50/) · , ·…
    Board 20232 marksshort answer
16. The British physicist Thomas Young explained the interference of light using the principle of superposition of waves. He observed the interference pattern on the screen, in his experimental set- double slit experiment. The two slits S1 and S2 were illuminated …
    Board 20221 markMCQ
17. (a) A parallel beam of light of wavelength 600 nm is incident normally on a slit of width 0.2 mm. If the resulting diffraction pattern is observed on a screen 1 m away, find the distance of (i) first minimum, and (i) second maximum, from the central maximum. O…
    Board 20221 markvery short
18. The principle of superposition is used to understand the phenomenon of interference of light waves. The principle states that at a particular point, the resultant displacement produced by a number of waves is the vector sum of the displacements produced by eac…
    Board 20221 markMCQ
19. In a Young’s double -slit experiment, the slits are separated by 0.28 mm and the screen is placed 1.4 m away. The distance between the central bright fringe and the fourth bright fringe is measured to be 1.2 cm. Determine the wavelength of light used in the ex…
    CBSE practice 2023-242 marksshort answer
20. In Young’s double slit experiment, the distance between the slits is 0.25mm and the screen is placed 1.0m away. A student uses monochromatic light of wavelength 500nm. Assertion (A): The fringe width observed on the screen will be 2.0mm. Reason (R): The fringe…
    Sample paper 2026-271 markAssertion-Reason

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