Question

The property of light which cannot be explained by Huygen's construction of a wavefront is:

• A. Refraction
• B. Reflection
• C. Diffraction
• D. Origin of spectra

Hint:

Huygen’s wave theory explains wave phenomena like diffraction and interference but fails to explain phenomena requiring quantum mechanics, such as the photoelectric effect and spectral emissions.

Answer 1

The Correct Option is D

Step 1: Understanding Huygens' Wave Theory

Huygens' wave theory describes how light propagates by treating every point on a wavefront as a secondary wave source. Using this principle, the laws of: Reflection , Refraction , Diffraction are successfully derived.

Step 2: Analyzing the Given Options

Reflection: Huygens' principle explains reflection by considering the secondary wavelets on the incident wavefront, which create the reflected wavefront.

Refraction: Huygens' principle explains refraction by stating that different parts of a wavefront move at different speeds when passing through media with different refractive indices.

Diffraction: Huygens' principle accounts for diffraction, as each point on a wavefront acts as a source of secondary wavelets, allowing light to bend around obstacles.

Step 3: Why Huygens' Principle Fails to Explain Spectra

The origin of spectral lines arises due to the emission and absorption of photons by atoms, which is best explained by quantum mechanics. Huygens' wave theory does not consider the particle nature of light or energy quantization, which are essential for understanding:

Atomic emission spectra , Blackbody radiation , Photoelectric effect

Since Huygens' theory only deals with the wave nature of light and not its quantum properties, it cannot explain the origin of spectra.

Thus, the correct answer is: \(\mathbf{D}\)

Answer 2

Step 1: Understanding Huygen's Principle
Huygen's Principle states that: "Every point on a wavefront acts as a source of secondary wavelets, and the new wavefront is the envelope of these secondary wavelets."
This principle successfully explains several fundamental properties of light, such as:

Reflection – using the laws of reflection.

Refraction – using Snell’s Law.

Diffraction – by considering secondary wavelets bending around edges.

 

Step 2: The Limitation
However, Huygen’s theory is purely wave-based. It cannot explain:

• The origin of spectra – which arises from the discrete energy levels in atoms and transitions of electrons between them.

These require the **quantum theory of light** (i.e., photons and quantized energy), which was later introduced by Planck, Einstein, and Bohr. Huygen's classical wave model doesn’t address this.

 

Step 3: Final Answer
\[ \boxed{\text{Option 4: Origin of spectra}} \]