9TH GRADE · LIGHT PHENOMENA
Refraction and total internal reflection
Law of refraction, index and speed of light in a medium.
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Basic Concepts
Refractive index
The absolute indicator is equal to the ratio of the speed of light in a vacuum to the speed of light in a medium.
A larger number means a lower speed of light in the medium and usually a stronger deviation to the normal.
Refraction of light
At the boundary of the media, the beam changes direction because the speed of light propagation changes.
When passing into an optically denser medium, the beam usually deviates towards the normal.
Total internal reflection
Light is completely reflected when leaving an optically denser medium at an angle greater than the critical one.
The phenomenon is used in optical fiber and prisms; it is impossible when falling from a less dense medium to a more dense one.
Physical quantities
Refractive index
The ratio of the speed of light in a vacuum to the speed in a medium.
Unit: dimensionless quantity
Speed of light
Speed of electromagnetic waves in vacuum.
Unit: meter per second ·
Speed of light in the medium
Speed of propagation of light in a transparent medium.
Unit: meter per second ·
Angle of refraction
The angle between the refracted ray and the normal to the surface.
Unit: radian ·
Lesson formulas
Law of refraction
The product of the medium index and the sine of the angle to the normal is preserved at the boundary.
Physical meaning of the indicator
The refractive index shows how many times the speed of light in a medium is less than vacuum.
Related formulas
The same formulas in the reference, with symbols and units.
Tasks on the topic
Statements, answer options and the walkthrough.