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CAIE A-Level Physics 7.5.2 Malus's Law

Practise applying Malus’s law I = I₀ cos²θ to one or more polarising filters, including intermediate and limiting intensities.

Syllabus
2028–2030
Course
Physics 9702
Level
AS

Exam points

  • calculate transmitted intensity with Malus’s law I = I₀ cos²θ for one or more filters
  • determine effective angle or intermediate intensity in a series of polarising filters
  • interpret how changing the angle between transmission axes changes transmitted intensity, including limiting cases

7.5.2—Malus’s law (I = I0 cos2θ ) to calculate the intensity of a plane-polarised question 1

[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 ]
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