A calcite crystal is placed over a dot on a piece of paper and rotated, on seeing through the calcite one will be see

A calcite crystal placed over an ink dot is rotated. On seeing through the crystal one finds

One cannot see through the fog because

Can any one see in the dark?

A tourmaline crystal is placed in the path of a polarised beam of light. If it is rotated through one complete rotation, what change will be observed in the intensity of the transmitted light?