Three Polaroid sheets

PHYSICS · Multi-part · AP · Physics 2: Algebra-based · Waves Sound and Physical Optics · Waves Sound and Physical Optics

Problem

P_1

P_2

and

P_3

are arranged coaxially. The transmission axis of

P_1

is vertical. The axis of

P_3

is horizontal (i.e. at

90^{\circ}

P_1

). The axis of the middle sheet

P_2

makes an angle

\phi

with the vertical. Unpolarised light of intensity

I_0

is incident normally on

P_1

. (a) Derive an expression for the intensity

I(\phi)

of light emerging from

P_3

in terms of

I_0

and

\phi

. (b) Determine the value of

\phi

for which the transmitted intensity is maximum, and calculate this maximum intensity. (c) For what value of

\phi

will the transmitted intensity be exactly

\dfrac{I_0}{8}

? (d) Give a qualitative explanation of why inserting

P_2

between two crossed Polaroids allows some light to pass, even though

P_1

and

P_3

alone would block all light.