Everyone knows or at least heard that light has the property of refracting and reflecting. But only the formulas of geometrical and wave optics can explain how, or rather on what basis, this happens. And all this teaching is based on the concept of "ray", which was introduced by Euclid three centuries before our era. So what is a beam, scientifically speaking?
A beam is a straight line along which light waves move. How, why - these questions are answered by the formulas of geometric optics, which is part of wave optics. The latter, as one might assume, treats rays as waves.
Formulas of geometric optics
The law of rectilinear propagation: a ray in a medium of the same type tends to propagate rectilinearly. That is, light travels along the shortest path that exists between two points. You could even say that the light beam seeks to save itself time. This law explains the phenomena of shadow and penumbra.
For example, if the light source itself is small in size or is located at such a large distance that itsizes can be ignored, the light beam forms clear shadows. But if the light source is large or very close, then the light beam forms fuzzy shadows and partial shadows.
Law of Independent Propagation
Light rays tend to propagate independently of each other. That is, they will not affect each other in any way if they intersect or pass through each other in some homogeneous medium. The rays seem to be unaware of the existence of other rays.
Law of Reflection
Let's imagine that a person points a laser pointer at a mirror. Of course, the beam will be reflected from the mirror and will propagate in another medium. The angle between the perpendicular to the mirror and the first ray is called the angle of incidence, the angle between the perpendicular to the mirror and the second ray is called the angle of reflection. These angles are equal.
The formulas of geometric optics reveal many situations that no one even thinks about. For example, the law of reflection explains why we can see ourselves in a "straight" mirror exactly as we are, and why its curved surface creates a different image.
Formula:
a - angle of incidence, b - angle of reflection.
a=b
The law of refraction
The ray of incidence, the ray of refraction and the perpendicular to the mirror are located in the same plane. If the sine of the incident angle is divided by the sine of the refraction angle, then the value n is obtained, which is constant for both media.
n shows at what angle the beam from the first medium passes into the second, and how the compositions of these media correlate.
Formula:
i - incident angle. r - refractive angle. n21 - refractive index.
sin i/sin r=n2/ 1= n21
Law of reversibility of light
What does the law of reversibility of light say? If the beam propagates along a well-defined trajectory in one direction, then it will repeat the same route in the opposite direction.
Results
The formulas of geometrical optics in a somewhat simplified form explain how a beam of light works. There is nothing difficult in this. Yes, the formulas and laws of geometric optics neglect some of the properties of the universe, but their importance to science cannot be underestimated.
