» Pulfrich Refractometer (0882)

Immagini

DESCRIPTION

Exhibit 882 is a Pulfrich refractometer. It consists of a glass cube KLMN (drawing 1) with a known index of refraction $Formula: [\mu_o]$ furnished by the constructor. The cube is fixed in an iron receptacle on three sides and on the brass base which is fixed to a metal support with three screws for leveling. The front side toward the telescope (T) is free to transmit the refracted light toward T. There is a small cylinder cemented on the top of the cube intended to contain the liquid of which one wants to determine the index of refraction μ. The cylinder has no bottom so the liquid is in direct contact with the cube. In practice, a ray of monochromatic light AO coming from a source S is incident on the cube in the point O at a grazing angle. The ray crosses the liquid of unknown index μ and then the cube, exiting in the direction BT, at an angle r respect to the vertical and entering the telescope pointed to infinity and furnished with an eyepiece. See drawing 1. No ray can exit from the cube at an angle greater than the maximum angle r. Thus upon rotating the telescope, one sees a neat separation between the dark and bright fields in the telescope corresponding to angles greater than or less than r. The angle r can be measured on the graduated scale between 0 and 90° with a resolution of one degree with the help of a vernier. One can use this method to determine the index of refraction of a substance only if $Formula: [\mu < \mu_o]$ .

One has:

Equazione: [\frac{\mu_o}{\mu}= \frac{sin(\pi/2)}{sin\ c}=\frac{1}{sin c}\eqno{1} ]

Equazione: [\mu_o = \frac{sin\ r}{sin(\pi/2 - c)}= \frac{sin\ r}{cos\ c}\eqno{2}]

Between the equations (1,2) one can eliminate c:

Equazione: [sin\ c = \frac{\mu}{\mu_o},\qquad cos\ c=\frac{sin\ r}{\mu_o}]

Therefore, squaring, summing and removing the denominators:

and finally:

Equazione: [ \mu = \sqrt {\mu_o^2 - sin^2 r }\eqno{3}]

$Formula: [\mu_o]$ is a characteristic constant of the instrument, r is read on the calibrated scale; from (3) one can calculate μ.

4 Images and one drawing

ISCRIZIONI

Su circolo è scritto "MAX WOLZ BONN N°2570

BIBLIOGRAPHY

[1] Eligio Perucca,"Fisica Generale e Sperimentale", Volume secondo, Torino, UTET ,1937. Pag. 336.
[2] Worsnop B.L., Flint H.T., "Advanced Practical Physics",Asia Publishing House, New Delhi, 1961. pagg.: 293-295.

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