Founding symbol: Planck published a paper on the energy distribution law of normal spectrum in the German Yearbook of Physics in 1900, which marked the birth of quantum theory.

1905, the quantum concept of Einstein Prize was extended to the propagation of light, and the quantum theory of light was put forward.

19 13 years, British physicist Bohr extended the concept of quantum to the internal energy states of atoms, and proposed a quantized atomic structure model, which enriched the quantum theory.

2. Thermal radiation phenomenon

Any object will emit electromagnetic waves of various wavelengths at any temperature, and its radiation energy and its distribution according to wavelength are related to temperature. The phenomenon that molecules and atoms in matter emit electromagnetic waves due to thermal excitation is called thermal radiation.

Objects radiate energy and absorb energy. The stronger an object's ability to emit electromagnetic waves in a certain frequency range, the stronger its ability to absorb electromagnetic waves in that frequency range.

3. Doppler effect

Due to the relative motion between the wave source and the observer, the phenomenon that the observer feels the frequency change is called Doppler effect. It was discovered by Austrian physicist Doppler in 1842.

The sound source completes a complete vibration and emits a wave of one wavelength. Frequency represents the number of complete vibrations per unit time, so the frequency of the wave source is equal to the number of complete waves emitted by the wave source per unit time, and the tone of the sound heard by the observer is determined by the frequency received by the observer, that is, the number of complete waves received per unit time.

4, the law of refraction of light

The refractive index of light entering the medium from vacuum is called the absolute refractive index of the medium, which is also referred to as the refractive index of the medium for short.

When light is injected from one medium into another, although the ratio of sine of incident angle to sine of refraction angle is a constant n, this constant n is different for different media. This constant n is related to the medium and is a physical quantity reflecting the optical properties of the medium. We call it the refractive index of the medium.

5. Total reflection of light

Total reflection phenomenon When light enters the light-sparse medium from the light-dense medium, the refraction angle is greater than the incident angle. When the incident angle increases to a certain angle, the refraction angle is equal to 90. At this time, the refracted light disappears completely, and all the incident light is reflected back to the original medium. This phenomenon is called total reflection.

When the light is incident on the end face of the optical fiber, it is refracted into the optical fiber, totally reflected at the interface between the inner core and the outer sheath for many times, and then emitted from the other end face of the optical fiber, and will not escape from the outer sheath, so the light energy loss is extremely small.