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EXPERIMENT NO. – 11

MALUS LAW

OBJECT:-To verify the Law of Malus for plane polarized light with the help of photovoltaic cell.
APPARATUS REQUIRED -

Optical bench, halogen lamp, double convex lens, polarizer, analyzer, photo voltaic cell with colorimeter and micro-ammeter (0-50mA).

FORMULA USED -

According to Malus Law, when a beam of completely plane polarized light is incident on the analyzer, then the intensity I of the emergent light is given by

I= I_o cos² ϕ

Where I_o = Intensity of plane polarized light incident on the analyzer.

Φ= angles between planes of transmission of polarizer and the analyzer

To verify this law, light from the analyzer is made to enter in a photovoltaic cell. The current output of photovoltaic dell is connected to microammeter.

PROCEDURE:-

The experimental setup is arranged as shown in the figure. In this arrangement, the source S, convex lens, Polarizer P, Analyzer A and the window of Photovoltaic cell should be at the same height.
Now switch on the incandescent bulb. Light from the source S rendered parallel with the help of convex lens L is allowed to fall on polarizer P.
For any orientation of the polarizer P, the polarized light passes through analyzer A. The analyzer A is rotated till there is maximum deflection in the micro-ammeter. The position of analyzer is noted on the circular scale. The corresponding micro-ammeter deflection is also recorded. The position of analyzer corresponds to ϕ=0 (here ϕ is the angle between Planes of transmission of polarizer and analyzer.)
The analyzer A is rotated through a small angle, say 10^o and then the steady micro-ammeter deflection is noted.
The experiment is repeated by rotating the analyzer through 10^o degree each time and noting down the corresponding micro-ammeter deflection till it become practically zero.

OBSERVATIONS:-

S. No.	Angles through which analyzer is rotated ϕ	Micro-ammeter reading		Cos ϕ	Cos²ϕ	θ/Cos²ϕ
S. No.	Angles through which analyzer is rotated ϕ	µA	θ	Cos ϕ	Cos²ϕ	θ/Cos²ϕ
1.	10^o
2.	20^o
3.	30^o
4.	40^o
5.	50^o
6.	60^o
7.	70^o
8.	80^o

CALCULATIONS:-

Find the value of θ/Cos²ϕ from each observation and plot the graph for cos²ϕ on X-Axis and θ on Y-Axis. Discuss the nature and reason for such a graph.

SOURCES OF ERROR AND PRECAUTIONS:-

1. The position of the polarizer should not be disturbed throughout the experiment.

2. The source of light, lens, polarizer, analyzer, and the solar cell should be adjusted to the same height.

3. The voltage applied to the light source should be constant throughout the experiment.

4. The experiment should be performed in the dark room to avoid any external light inside the photovoltaic cell.

5. Care should be taken while performing the experiment as the bulb becomes very hot.