Polarisation is a phenomenon associated with light waves but not with sound waves.
State the meaning of polarisation.
State why light waves can be plane polarised but sound waves cannot.
Two polarising filters A and B are positioned so that their planes are parallel to each other and perpendicular to a central axis line XY, as shown in the figure below.
The transmission axis of filter A is vertical and the transmission axis of filter B is horizontal. Unpolarised light of a single frequency is directed along the line XY from a source positioned at X. The light emerging from filter A is vertically plane polarised and has intensity 
.
Filter B is rotated from its starting position about the line XY, as shown in the figure. After rotation, the intensity of the light emerging from filter B is 
. Calculate the angle of rotation of filter B from its starting position.
and the angle of rotation is 
or 
.
