Light from a sodium lamp (S) passes through two polaroid sheets ${\mathit{P}}_1$ and ${\mathit{P}}_2$ as shown in fig. What will be the effect on the intensity of the light transmitted (a) by ${\mathit{P}}_1$ and (b) by ${\mathit{P}}_2$ on rotating polaroid ${\mathit{P}}_1$ about the direction of propagation of light? Justify your answer in both cases.
OR
Define the term 'wavefront of light'. A plane wave front $\mathit{A}\mathit{B}$ propagating from denser medium (1) into a rarer medium (2) is incident on the surface ${\mathit{P}}_1{\mathit{P}}_2$ separating the two media as shown in fig.
Using Huygen's principle, draw the secondary wavelets and obtain the refracted wavefront in the diagram.