The interference of light is a manifestation of the fluctuation of light. If the light emitted by the same light source is divided into two beams, each beam will meet again after passing through different paths. When the optical path difference is less than the coherent length of the light source, interference will generally occur. Interference is widely used in scientific research and industrial technology, such as measuring the wavelength of light waves, accurately measuring the length, thickness and angle.

If the wavelength of monochromatic light source is known, the curvature radius R of plano-convex lens can be calculated only by measuring the radius rm of the first dark ring, while if R is known, the wavelength of incident monochromatic light wave can be calculated after measuring rm.

Because the convex surface of the plano-convex lens can't be in ideal point contact with the plane of the optical flat glass, the contact pressure will cause local elastic deformation, making the contact place a circular plane, and the center of the interference ring is a dark spot or there is dust in the air gap layer, which adds an optical path difference to the dark ring formula.

Extended data:

Precautions:

1. It is necessary to design an experimental data record table. The original data records shall not be filled in with pencil, and shall not be altered in large quantities. After the experiment is completed, it must be signed by the instructor.

2. General equipment should be listed briefly, and the instrument model, specification and manufacturer should be explained. Some valuable instruments should be simply marked with precautions and put in brackets.

3. Design some questions for students to think and deduce, and avoid copying books. The principle part of the experimental report is graded according to the completion of this part.

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