Huygens Principle - UNSOLVED PRACTICE SET
Chapter: Wave Optics | Topic: Huygens Principle
HUYGENS PRINCIPLE - UNSOLVED PRACTICE SET
Topic: Huygens Principle
Multiple Choice Questions
Q1. According to Huygens' principle, each point on a wavefront acts as:
- A sink for light energy
- A source of secondary wavelets
- A barrier to light propagation
- A point of destructive interference
Q2. The shape of the wavefront from a point source of light in an isotropic medium is:
- Plane
- Cylindrical
- Spherical
- Parabolic
Q3. Huygens' principle can be used to explain:
- Only reflection of light
- Only refraction of light
- Reflection, refraction, and interference of light
- Only the particle nature of light
Q4. The envelope of secondary wavelets gives:
- The position of the source
- The new position of the wavefront
- The intensity of light at a point
- The wavelength of light
Q5. For a plane wavefront travelling in vacuum, the secondary wavelets are:
- Spherical with different radii
- Spherical with the same radius
- Cylindrical with varying radii
- Elliptical in shape
Q6. Huygens' principle assumes that:
- Light travels as particles
- Light is a transverse wave
- Every point on a wavefront is a source of secondary wavelets
- Light requires a material medium for propagation
Short Answer Questions
Q7. State Huygens' principle. What is a wavefront?
Q8. Distinguish between a plane wavefront, a spherical wavefront, and a cylindrical wavefront. Give one example of each.
Q9. Using Huygens' principle, explain how a plane wavefront propagates through a homogeneous medium.
Q10. Why does Huygens' principle fail to explain the phenomenon of photoelectric effect?
Q11. Draw a diagram showing secondary wavelets originating from a spherical wavefront. How does the new wavefront form?
Q12. What is the geometrical shape of the wavefront when light from a distant star reaches the Earth? Explain why.
Long Answer Questions
Q13. State Huygens' principle and use it to explain the propagation of a plane wavefront through a homogeneous medium. Draw appropriate diagrams.
Q14. Explain the construction of a new wavefront using Huygens' principle. How does this construction help in understanding the laws of reflection and refraction?
Q15. Discuss the limitations of Huygens' principle. Why was it necessary to modify Huygens' principle into Huygens-Fresnel principle?
Numerical & Application-Based Problems
Q16. A point source of light emits waves in all directions. At time t = 0, the wavefront is at a distance of 1 m from the source. The speed of light in the medium is 2 ร 10โธ m/s.
(a) Calculate the radius of the wavefront at t = 2 ฮผs.
(b) Calculate the radius of the wavefront at t = 5 ฮผs.
(c) Draw a diagram showing the wavefronts at these two instants.
(d) Calculate the wavelength if the frequency of light is 5 ร 10ยนโด Hz.
Q17. A plane wavefront is incident on a boundary separating two media. The speed of light in the first medium is 3 ร 10โธ m/s and in the second medium is 2 ร 10โธ m/s. The angle of incidence is 30ยฐ.
(a) Using Huygens' construction, show how the refracted wavefront is formed.
(b) Calculate the angle of refraction.
(c) If the wavelength in the first medium is 600 nm, calculate the wavelength in the second medium.
Q18. In your school's physics lab, a student sets up a ripple tank to study wave propagation.
(a) She generates circular waves using a point source. The waves travel at 0.3 m/s. After 2 seconds, she draws the wavefront. Calculate the radius of this wavefront.
(b) She then places a straight barrier in the tank and observes the reflection of plane waves. Using Huygens' principle, explain why the angle of reflection equals the angle of incidence. Draw a diagram showing secondary wavelets from the reflecting surface.
(c) The student replaces the straight barrier with a concave reflector. Explain using Huygens' principle why the reflected waves converge to a point.
(d) A classmate argues that Huygens' principle cannot explain why light travels in straight lines. Present your counter-argument using Huygens' construction for a plane wavefront.