According to huygen's theory of secondary waves, following can be explained

Options

A. propagation of light
B. the wavelength of light
C. refraction of light
D. all of the above

Answer

### Step-by-Step Text Solution:

1. **Understanding Huygen's Principle**: Huygen's principle states that every point on a wavefront can be considered as a source of secondary wavelets. These wavelets spread out in the forward direction at the same speed as the original wave.

2. **Formation of New Wavefront**: The new wavefront is formed by the envelope of these secondary wavelets. This means that the new wavefront is tangent to all the wavelets emitted from the points on the previous wavefront.

3. **Application of Huygen's Principle**: Huygen's principle can be used to explain various optical phenomena such as reflection, refraction, and interference of light waves.

4. **Reflection**: When light reflects off a surface, the angle of incidence is equal to the angle of reflection. Huygen's principle helps visualize how the wavefront changes direction upon reflection.

5. **Refraction**: In refraction, when light passes from one medium to another, the change in speed causes the wavefront to bend. Huygen's principle allows us to understand how the wavefront is altered at the boundary between two different media.

6. **Interference**: The principle also explains interference patterns created by overlapping wavefronts from different sources. The superposition of wavelets leads to constructive and destructive interference.

7. **Propagation of Light**: Huygen's principle describes the propagation of light through a medium, which is assumed to be luminiferous (able to carry light waves).

8. **Conclusion**: Therefore, according to Huygen's theory of secondary waves, the phenomena of reflection, refraction, and interference can be effectively explained. The correct option that summarizes these explanations is option D.