Flat plate

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The flat plate or plane parallel plate is one of the optical components .

Parallel displacement on a plane plate

Image plane offset

The plane plate cannot produce its own image like a lens . However, it can shift the position of the image plane of an image depending on the plate thickness and the refractive index :

If a plane plate is introduced into the image space of a beam path perpendicular to the optical axis, the image plane is increased by the amount

shifted towards the imaging lens . This applies to a good approximation for small "opening angles" where the tangent can be set equal to the sine of this angle.

This image plane offset can be measured and used to easily determine the refractive index of the plane plate, whereby the refractive index of the air is included:

The effect can be easily observed in aquariums , for example , where there is a thick layer of water between the object and the viewer (in addition to the glass wall of the aquarium).

Parallel shift

At oblique incidence of a light beam undergoes at both interfaces of the plane plate refraction . The exit angle is the same as the entry angle and the exit cross-section is the same as the entry cross-section of the jet. The exiting beam is shifted by the distance parallel to the incident beam . It applies

The parallel displacement increases when the thickness of the plate, the angle of incidence or the refractive index of the plate medium is increased.

Ophthalmometer according to Hermann von Helmholtz

The Ophthalmometer by Hermann von Helmholtz uses the principle of the parallel offset. It can be used to determine the distance between two points. It is also possible to measure the point spacing on a curved surface (for example the cornea of ​​an eye).

Reflective properties

literature

  • Ludwig Bergmann, Clemens Schaefer: Textbook of Experimental Physics . 10th edition. Volume 3 - Optik, Walter de Gruyter, 2004, ISBN 978-3-11-017081-8 .

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