2 Experimental setup
The laboratory setup to test Malus law is shown in Figure 3.12. Elements of the installation: 1 - source of natural light (Incandescent), 3 - polarizer, 4 - Analyzer, 6 - photocell barrier layer 7 - microammeter. All elements of the installation parts are fixed in special raters in order that they can be moved along the optical bench. Polarizer and the analyzer can be rotated around the axis 00ꞌ. For measuring angles in frames raters polarizer and analyzer have special limbs with a scale.
Figure 3.12. The experimental scheme
The laboratory setup to test Malus law is shown in Figure 3.12. Elements of the installation: 1 - source of natural light (Incandescent), 3 - polarizer, 4 - Analyzer, 6 - photocell barrier layer 7 - microammeter. All elements of the installation parts are fixed in special raters in order that they can be moved along the optical bench. Polarizer and the analyzer can be rotated around the axis 00ꞌ. For measuring angles in frames raters polarizer and analyzer have special limbs with a scale.
Polarizer and the analyzer, which is used in this experiment, are the polaroids. Each of them is a thin film made of celluloid, which consist of thin crystals of gerpatit. Natural light passing through these crystals split into ordinary and extraordinary rays polarized in mutually perpendicular planes. The gerpatit also has the property of dichroism. All ordinary rays are completely absorbed by the thin film of gerpatit's crystal thickness 0.1-0.3 mm. Through gerpatit can pass only the extraordinary rays. Thus, the natural light falling on the gerpatit's film turns at the output in a linearly polarized light.
Photocurrent on the microammeter is proportional to the light flux incident to the photocell or intensity of light, that transmitted through the analyzer i = kIi Maximum of fotocurrent corresponds to the maximum intensity imax= kI0.
According to the law of Malus is possible with parallel nicols, ie θ = 0. To any other provisions of Nicol is fulfilling relationship.
From the law of Malus follows that
Ii /I0 = cos2θ.
Can theoretically calculate the dependence of Ii/I0 = fT (cos2θ), construct its graph and compare with the graph of the experimental dependence Ii/I0 = fe(cos2θ).
The coincidence of graphs confirms the validity of the law of Malus.
2.1 Order of experiment’s performance
1. Install all devices on the optical bench, as shown in Figure 3.12.
2. Turn on the light source, adjust the height of all devices so that the light beam will pass through the all devices and will fall on the photocell.
3. Turn off the light source, connect the photocell circuit and record electrical current of photocell i0. Weak photocurrent i0 caused by exposure to a photocell extraneous light sources in the room.
4. Install the Limbo of analyzer to zero division. Turn on the light source S.
Smoothly rotate the polarizer to achieve the maximum deflection of the microammeter im. Here, obviously, the plane of polarization of the polarizer and analyzer are parallel to each other, i.e. the angle between them is zero.
5. No more changing the position of the polarizer, rotate the analyzer in the range of 0° to 360°, recording every 15° angle θ and a corresponding photocurrent i in column 2 of Table 3.1.
6. Repeat step 5 two times, write the value of the photocurrent i in columns 3 and 4 of Table 3.1. Table 3.1 – Checking the law of Malus
θ град |
i1 mA |
i2 mA |
i3 mA |
mA |
|
cos |
cos2 |
0 |
|
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|
15 |
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|
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|
30 |
|
|
|
|
|
|
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… |
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|
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|
|
|
|
345 |
|
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