VERIFY MALUS’ LAW FOR LINEARLY POLARISED LIGHT
Theory:
Light is a transverse electromagnetic wave. Thus, Let the electric field vector of
⃗⃗⃗⃗ . The component of 𝐸
⃗⃗⃗⃗ Perpendicular to the analyzer
the first transmitted beam 𝐸
⃗⃗⃗⃗ parallel to the analyzer axis,
axis is completely absorbed. The component of 𝐸
which is transmitted through the analyzer, is 𝐸 cos 𝜃
In this experiment light passes through two filters termed the polarizer and the
analyzer, which are aligned at an angle of to one another. The polarizer only
allows one linearly polarized component of the light to pass through it. The
electric field of this component has an amplitude .
The amplitude of the component after passing through the analyzer filter is given
by
This is a measure of the amount of light which can pass through the analyzer
(Fig. 1).
(Fig. 1)
We can verify Malus’ law which states that when completely plane polarized light
is incident on the analyzer, the intensity of the light transmitted by the analyzer
is directly proportional to the square of the cosine of angle between the
transmission axes of the analyzer and the polarizer.
1
𝑰
𝑰 𝒄𝒐𝒔
𝑴𝒂𝒍𝒖𝒔’𝒔 𝒍𝒂𝒘
where 𝑰 is the intensity of light after passing through the polarizer.

When θ = 90°,
0 That is the intensity of light transmitted by
the analyzer is minimum when the transmission axes of the analyzer and polarizer
are perpendicular to each other.

When θ = 0° ( or 180° ),
0 That is the intensity of light
transmitted by the analyzer is maximum when the transmission axes of the
analyzer and the polarizer are parallel.
Equipment:
• Metallic optical bench.
• Scaled Polarizer 360° with holder.
• Analyzer.
• Laser with holder.
• Lux meter with holder.
SET-UP AND PROCEDURE
1. Set up the apparatus for the measurement as shown in Fig. 1.
2. Set both polarization filters to 0° with the help of the angle scale and
record the corresponding light intensity.
Note: The polarization filter nearest the optical lamp acts as the polarizer and the
one nearer the light sensor is used as the analyzer.
3. Adjust the analyzer in 10° steps up to and including 90° and, for each of these
angle settings, record the light intensity in table.
4. Plot light intensity against
𝜃 on a graph.
5. The measurement values lie along a straight line of gradient
origin, as expected from equation (2).
0
through the
6. Determine the slope of the straight line to get the value 𝑰0 from the graph.
2
𝒄𝒐𝒔
𝑰 (Lux)
10
20
30
40
50
60
70
80
90
3