Class 12 Wave Optics IMPORTANT QUESTIONS for 2024-2025

Wave Optics - Important Questions

Multiple Choice Questions (MCQs):

1. Which of the following phenomena is explained by Huygens' principle?
a) Photoelectric effect
b) Reflection and refraction
c) Compton effect
d) Raman effect

2. In Young’s double slit experiment, the fringe width increases if:
a) The wavelength of light decreases
b) The distance between the slits increases
c) The distance between the screen and the slits decreases
d) The wavelength of light increases

3. The ratio of intensities of two waves interfering at a point is 9:4. The ratio of the amplitudes of the two waves is:
a) 3:2
b) 2:3
c) 9:4
d) 4:9

4. In Young's double slit experiment, coherent sources are required for sustained interference because:
a) They have different wavelengths
b) They maintain a constant phase difference
c) They have different frequencies
d) They produce high intensity light

5. The angular width of the central maximum in a single slit diffraction pattern is:
a) Directly proportional to the slit width
b) Inversely proportional to the slit width
c) Directly proportional to the wavelength of light
d) Inversely proportional to the wavelength of light

6. The condition for sustained interference of light waves is:
a) The sources must be incoherent
b) The sources must be coherent
c) The sources must be of different wavelengths
d) The sources must have different frequencies

7. In Young’s double slit experiment, the distance between the slits is doubled. The fringe width will:
a) Remain the same
b) Be doubled
c) Be halved
d) Become four times

8. The phenomenon where light bends around the corners of an obstacle is called:
a) Interference
b) Diffraction
c) Reflection
d) Refraction

9. The wavelength of light used in Young's double slit experiment is 600 nm. If the distance between the slits is 0.3 mm, and the distance between the slits and the screen is 1.5 m, the fringe width is:
a) 3 mm
b) 2 mm
c) 1 mm
d) 0.5 mm

10. In a single slit diffraction experiment, if the width of the slit is halved, the width of the central maximum will:
a) Be halved
b) Be doubled
c) Remain the same
d) Become four times

Subjective Questions:

1. Explain the concept of wavefront. Using Huygens’ principle, derive the laws of reflection.

2. Using Huygens’ principle, explain the refraction of a plane wavefront at a plane surface.

3. State Young’s double slit experiment and provide the expression for fringe width.

4. What is meant by coherent sources? Why are coherent sources necessary for sustained interference?

5. Describe the phenomenon of diffraction of light through a single slit. Provide a qualitative treatment of the width of the central maximum.

6. In Young’s double slit experiment, how does the fringe width change if the whole apparatus is immersed in water? Explain with reasons.

7. Explain how interference patterns are formed in Young’s double slit experiment. What conditions are necessary for observing these patterns?

8. A light wave traveling in air is incident on a glass slab at an angle of 30°. Using Huygens’ principle, explain the change in the wavefront as it enters the glass slab.

9. Derive the relationship between the angle of incidence and the angle of refraction using Huygens’ principle.

10. In a Young’s double slit experiment, the distance between the slits is 0.5 mm, and the distance between the slits and the screen is 2 m. If the wavelength of light used is 500 nm, calculate the fringe width.

11. Calculate the angular width of the central maximum in a single slit diffraction pattern where the slit width is 0.1 mm and the wavelength of light used is 600 nm.

12. Two coherent sources of intensity ratio 4:1 produce an interference pattern. Calculate the ratio of the maximum to the minimum intensity in the interference pattern.

13. Light of wavelength 600 nm is incident on a single slit of width 0.2 mm. Calculate the distance between the first and the second dark fringes on a screen 2 m away.

14. In a Young's double slit experiment, the separation between the slits is 0.25 mm and the screen is placed 1.5 m away. The distance between the central bright fringe and the fourth bright fringe is 1.2 cm. Calculate the wavelength of the light used.

15. If in Young’s double slit experiment, the distance between the slits and the screen is doubled and the wavelength of the light is halved, what will be the effect on the fringe width?

16. A parallel beam of light of wavelength 500 nm is incident on a single slit of width 0.2 mm. Calculate the angular width of the central maximum.

17. Two slits in Young's double slit experiment have widths in the ratio 1:4. What will be the ratio of the intensities of the bright fringes produced by these slits?

18. In a Young's double slit experiment, the slits are separated by 0.4 mm and the screen is placed 1 m away. If the distance between the central bright fringe and the first bright fringe is 2.5 mm, calculate the wavelength of the light used.

19. Calculate the width of the central maximum in a single slit diffraction pattern if the wavelength of light used is 600 nm and the slit width is 0.15 mm, and the screen is placed 2 m away.

20. In a double slit experiment, light of wavelength 600 nm produces fringes of width 0.8 mm on a screen placed 2 m away from the slits. Calculate the distance between the slits.