Answer, in brief, any one question: a) Explain with proper sketch, the differences between wavefronts and wavelets. b) What is polarizing angle? Does it depend on wavelength of light used?

Answer (a): Wavefronts and wavelets are key concepts in wave propagation.

• Wavefronts are imaginary surfaces where all points on the surface vibrate in phase (same phase). They are represented by larger circles (or spherical surfaces in 3D) and indicate the position of the wave at a given time. For example, in the figure, the large circles represent wavefronts of a wave emanating from a point source $S$.

• Wavelets are small wave segments originating from each point on a wavefront. They are represented by smaller circles (or spherical surfaces) and show how the wave propagates forward. Each wavelet interferes constructively with others to form the next wavefront.

In summary, wavefronts are the envelopes of wavelets, and wavelets are the building blocks that construct the wavefronts. The figure above illustrates this difference clearly.