Refraction and Reflection using Huygens Principle - UNSOLVED PRACTICE SET
Chapter: Wave Optics | Topic: Refraction and Reflection using Huygens Principle
REFRACTION AND REFLECTION USING HUYGENS PRINCIPLE - UNSOLVED PRACTICE SET
Topic: Refraction and Reflection using Huygens Principle
Multiple Choice Questions
Q1. Using Huygens' principle, the laws of reflection can be explained by considering:
- The interference of secondary wavelets
- The construction of the reflected wavefront from secondary wavelets
- The diffraction of light at the reflecting surface
- The polarization of reflected light
Q2. When a plane wavefront is refracted from a rarer to a denser medium:
- The wavelength increases and the wavefront bends away from the normal
- The wavelength decreases and the wavefront bends towards the normal
- The wavelength remains unchanged and the wavefront bends towards the normal
- The frequency decreases and the wavefront bends away from the normal
Q3. The speed of light in a medium is related to the speed in vacuum by:
- v = c ร n
- v = c / n
- v = c + n
- v = c โ n
Q4. During refraction, which property of light does NOT change?
- Wavelength
- Speed
- Frequency
- Direction
Q5. According to Huygens' construction for reflection, the reflected wavefront is:
- Perpendicular to the incident wavefront
- Parallel to the incident wavefront
- At the same angle to the normal as the incident wavefront
- At twice the angle of the incident wavefront
Q6. The bending of a wavefront at an interface between two media is due to:
- Change in frequency
- Change in speed of the wave
- Change in amplitude
- Change in polarization
Short Answer Questions
Q7. Using Huygens' principle, explain the law of reflection of light. Draw a diagram showing the incident and reflected wavefronts.
Q8. Using Huygens' principle, derive Snell's law of refraction. Draw a diagram showing the incident and refracted wavefronts.
Q9. Why does the wavelength of light change when it enters a different medium, but the frequency remains constant?
Q10. A plane wavefront is incident on a plane mirror at an angle of 30ยฐ. Draw a diagram showing the reflected wavefront using Huygens' construction.
Q11. Explain why the refracted wavefront bends towards the normal when light enters an optically denser medium.
Q12. Using Huygens' principle, show that the angle of incidence equals the angle of reflection for a plane mirror.
Long Answer Questions
Q13. Using Huygens' wave theory, derive the laws of reflection. Draw a neat diagram showing the incident wavefront, the reflecting surface, and the reflected wavefront.
Q14. Using Huygens' construction, derive Snell's law of refraction for a plane wavefront incident on a plane interface separating two media. Explain each step with a diagram.
Q15. Explain how Huygens' principle accounts for the change in wavelength when light passes from one medium to another. Show that ฮปโ/ฮปโ = vโ/vโ = nโ/nโ.
Numerical & Application-Based Problems
Q16. A plane wavefront is incident on a plane boundary separating air (n = 1) and glass (n = 1.5) at an angle of incidence of 45ยฐ. The wavelength of light in air is 600 nm.
(a) Using Huygens' construction, calculate the angle of refraction.
(b) Calculate the speed of light in glass.
(c) Calculate the wavelength of light in glass.
(d) Calculate the frequency of light and verify that it remains unchanged.
Q17. A plane wavefront is incident on a plane mirror at an angle of incidence of 40ยฐ. The speed of light in air is 3 ร 10โธ m/s.
(a) Draw a diagram showing the incident and reflected wavefronts using Huygens' construction.
(b) Show that the angle of reflection is 40ยฐ.
(c) If the distance between successive wavefronts in air is 500 nm, calculate the frequency of the light.
(d) Explain why the reflected wavefronts remain in air and do not enter the mirror.
Q18. In your school's science fair, a student demonstrates refraction using a glass tank filled with water.
(a) She shines a laser beam from air into water at an angle of 50ยฐ. The refractive index of water is 4/3. Calculate the angle of refraction using Huygens' principle approach.
(b) She marks the positions of three successive wavefronts in air, spaced 2 cm apart. Calculate the spacing between these wavefronts in water.
(c) The student then places a glass slab (n = 1.5) in the water. Calculate the angle of refraction when light travels from water to glass at an angle of incidence of 30ยฐ.
(d) A classmate argues that since light slows down in water, it must lose energy. Explain why this reasoning is incorrect and what actually happens to the energy of the wave.
(e) In India, many ancient temples have stepped wells with water at the bottom. Explain why the steps appear shallower than they actually are when viewed from above the water surface, using the concept of refraction.