# Important Questions and Answers: Nature and Propagation of Light

1.  What is wavefront and wavelet?

Ans: The locus of vibrating particles in medium travelling in some phase at that instant is called wavefront. The new spherical wave originating from wavefront of the wave which travels with the speed of wave at that medium is called wavelet.

2. Diferentiate between plane wavefront and spherical wavefront.

Ans: If the source of light is point source, then the locus formed at  any instant is called the spherical wave front. If the source of light is in infinite distance, then the wavefront formed is called plane wavefront.

3. How can we change spherical wavefront to plane wavefront and vice versa?

Ans: We can interchange from one form to another form by using convex lens. When a spherical wavefront is kept at the focus of the lens, it changes into plane wavefront. Likewise if convex lens is kept in the path of plane wavefront, spherical wavefront is formed.

4. What are the advantages of Foucault’s method over Fizeau’s method of measure speed of light?

Ans: The advantages of  Foucault’s method over Fizeau’s method are:

• Foucault’s method can be applied in any optical medium while Fizeau’s method can be applied only in light or vacuum.
• Experiment setup for Foucault’s method can be conducted in a small laboratory while that of Fizeau’s method needs large distance of around 10-12 km.

5. Which parameter of light doesn’t changes on refraction?

Ans: When light undergo refraction, velocity and wavelength of light changes but its frequency remains constant. So, frequency is the fundamental property of light.

6. Explain Huygen’s principle.

Ans:  Huygen’s principle states that:

• Each light source sends out disturbance in all directions that travels in medium called ether medium.
• Light is a longitudinal wave.
• Different colors of light is due to the difference in wavelength.

7. What suggest the dual nature of light?

Ans: The phenomenon like reflection, refraction suggest that light behave like particle while phenomenon like interference, diffraction, polarization suggest that light can behave like wave. So, light is believed to have dual nature.

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#### One Response to “Important Questions and Answers: Nature and Propagation of Light”

1. amin khan

Obtain transmission and reflection coefficient of parallel polarized wave incident between conductor-conductor boundary with an oblique incidence.?