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CAIE A-Level Physics AS 7.5 Polarisation Questions

Practise explaining polarisation as evidence for transverse waves and calculating transmitted intensity through single or multiple filters with Malus’s law.

Syllabus
2028–2030
Course
Physics 9702
Level
AS

Exam points

  • explain polarisation as evidence of transverse-wave behaviour and distinguish it from longitudinal behaviour
  • calculate and interpret transmitted intensity through polarising filters with Malus’s law, including multiple filters

Covered syllabus points

7.5.1—Polarisation is a phenomenon associated with transverse waves7.5.2—Malus’s law (I = I0 cos2θ ) to calculate the intensity of a plane-polarised

Question 1

[Maximum number: 5]

Question (a)

(a)

Polarisation is a phenomenon associated with light waves but not with sound waves.

[ 2 ]

Question (i)

(i)

State the meaning of polarisation.

[ 1 ]

Question (ii)

(ii)

State why light waves can be plane polarised but sound waves cannot.

[ 1 ]

Question (b)

(b)

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 Fig. 4.1.

Fig. 4.1

Fig. 4.1

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 I0I_{0}.

Filter B is rotated from its starting position about the line XY , as shown in Fig. 4.1. After rotation, the intensity of the light emerging from filter B is 14I0\frac{1}{4} I_{0}.

Calculate the angle of rotation of filter B from its starting position.
angle of rotation = ∘{ }^{\circ}

[ 3 ]

Question 2

[Maximum number: 4]

Question (a)

(a)

A beam of vertically polarised light is incident normally on a polarising filter, as shown in Fig. 5.1.

Fig. 5.1

Fig. 5.1

[ 4 ]

Question (i)

(i)

The transmission axis of the filter is initially vertical. The filter is then rotated through an angle of 360∘360^{\circ} while the plane of the filter remains perpendicular to the beam.

On Fig. 5.2, sketch a graph to show the variation of the intensity of the light in the transmitted beam with the angle through which the transmission axis is rotated.

Fig. 5.2

Fig. 5.2

[ 2 ]

Question (ii)

(ii)

The intensity of the light in the incident beam is 7.6Wm−27.6 \mathrm{Wm}^{-2}. When the transmission axis of the filter is at angle θ\theta to the vertical, the light intensity of the transmitted beam is 4.2Wm−24.2 \mathrm{Wm}^{-2}.

Calculate angle θ\theta.

[ 2 ]

Question 3

[Maximum number: 5]

A beam of vertically polarised monochromatic light is incident on a polarising filter, as shown in Fig. 5.1.

Fig. 5.1

Fig. 5.1

The transmission axis of the filter is initially vertical and the transmitted light beam has the same intensity as the incident light beam.

The filter may be rotated about the direction of the light beam to change the angle of the transmission axis to the vertical.

Question (a)

(a)

State one angle of the transmission axis to the vertical that results in no transmitted light beam.

angle =

∘{ }^{\circ}

[ 1 ]

Question (b)

(b)

The filter is now positioned with its transmission axis at angle θ\theta to the vertical, as shown in Fig. 5.2.

Fig. 5.2

Fig. 5.2

The ratio  intensity of transmitted light  intensity of incident light \frac{\text { intensity of transmitted light }}{\text { intensity of incident light }} is equal to 0.75 .

[ 4 ]

Question (i)

(i)

Calculate angle θ\theta.

θ=\theta=
[ 2 ]

Question (ii)

(ii)

Calculate the ratio
> amplitude of transmitted light amplitude of incident light

ratio =
[ 2 ]
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