El Experimento De Fresnel

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Fresnel’s equations – Theory of reflection

LEP 2.5.03

Related topics Electromagnetic theory of light, reflection coefficient, reflection factor, Brewster’s law, law of refraction, polarization, polarization level. Principle and task Plane-polarized light is reflected at a glas surface. Both the rotation of the plane of polarization and the intensity of the reflected light are to bedetermined and compared with Frewsnel’s formulae for reflection. Equipment Laser, He-Ne 1.0 mW, 220 V AC Polarising filter, on stem Prism, 60 degrees, h 36.4 mm, flint Prism table with holder Photoelement f. opt. base plt. Protractor scale with pointer Articulated radial holder Stand tube Tripod base -PASSH-base -PASSRight angle clamp -PASSSupport rod -PASS-, square, l 400 mm Support rod -PASS-,square, l 250 mm Support rod -PASS-, square, l 630 mm Multirange meter with amplifier Dry cell, 1.5 V

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Problems 1. The reflection coefficients for light polarized perpendicular and parallel to the plane of incidence areto be determined as a function of the angle of incidence and poltted graphically. 2. The refractive index of the flint glass prism is to be found. 3. The reflection coefficients are to be calculated using Fresnel’s formulae and compared with the measured curves. 4. The reflection factor for the flint glass prism is to be calculated. 5. The rotation of the polarization plane for plane polarizedlight when reflected is to be determined as a function of the angle of incidence and presented graphically. It is then to be compared with values calculated using Fresnel’s formulae. Set-up and procedure The experimental set-up is as shown in Fig. 1. In this respect, the following information should be noted: A Setting up the swivel device 1. The pointer must first be screwed into the stand tube withits red tip pointing upwards. The stand tube is then inserted into the articulated radial holder until it reaches the stop and then tightened. The lower end of the stand tube is fastened in the tripod base. Caution: Never look directly into a non attenuated laser beam

Fig. 1: Experimental set-up for the determination of the rotation of the plane of polarization by reflection.

PHYWE seriesof publications • Laboratory Experiments • Physics • PHYWE SYSTEME GMBH • 37070 Göttingen, Germany

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LEP 2.5.03

Fresnel’s equations – Theory of reflection

2. The prism table, at which the protractor scale has been fixed, is fastened in the stand tube so that it can easily rotate but cannot wobble. 3. The support rods are fastened in the H-feet with the edge pointingupwards and joined to the articulated radial holder. The pointer and the longitudinal edge of the protractor scale should line up with the upper edge of the support rods (see Fig. 2). This can be easily carried out by turning the tripod base. 4. Finally, the clamping screw on the articulated radial holder is tightened slightly.

placed on the table with its reflecting surface centrally positioned sothat the incident beam is reflected back along its own path (Fig. 2). C Carrying out the measurements 1. After the laser has warmed up for about 15 minutes, the primary intensity io" of the beam polarized parallel to the plane of incidence is found. The laser is located in the normal position. Then the prism should be placed in position as in section B 3. After that, the angle of incidence ischanged in steps of 5 ° from ≤ 10° and a step angle of 1 ° should be selected in the region of the Brewster angle. The photocell is swivelled to obtain the maximum current for the determination of the intensity ir". Then the laser is turned through 90 ° and fixed on one of the legs on the H-base using the short support rod. The laser light is now oscillating normally polarized to the prism’s plane...