Light from a sodium lamp (S) passes through two polaroid sheets $P_1$ and $P_2$ as shown in fig. What will be the effect on the intensity of the light transmitted (a) by $P_1$ and (b) by $P_2$ on rotating polaroid $P_1$ about the direction of propagation of light? Justify your answer in both cases. OR Define the term 'wavefront of light'. A plane wave front $A B$ propagating from denser medium (1) into a rarer medium (2) is incident on the surface $P_1 P_2$ separating the two media as shown in fig. Using Huygen's principle, draw the secondary wavelets and obtain the refracted wavefront in the diagram.