Physics

State of matter

  • solid
  • liquid
  • gas
  • plasma

Metastability

Melting point

Supercooling

Superheating

boiling retardation

Classical mechanics

Power (功率)

power is the amount of energy transferred or converted per unit time. In the International System of Units, the unit of power is the watt, equal to one joule per second.

  • Formula of Power: P = E/t

Electromagnetism

Electromagnetic radiation (电磁波)

In physics, electromagnetic radiation (EMR) consists of waves of the electromagnetic (EM) field, which propagate through space and carry momentum and electromagnetic radiant energy. It includes radio waves, microwaves, infrared, (visible) light, ultraviolet, X-rays, and gamma rays. All of these waves form part of the electromagnetic spectrum.

Radio wave (无线电波)

Radio waves are a type of electromagnetic radiation with the longest wavelengths in the electromagnetic spectrum, typically with frequencies of 300 gigahertz (GHz) and below.

Radio waves were first predicted by the theory of electromagnetism proposed in 1867 by Scottish mathematical physicist James Clerk Maxwell.

Equivalently, the distance a radio wave travels in a vacuum, in one second, is 299,792,458 meters (983,571,056 ft), which is the wavelength of a 1 hertz radio signal.

Attenuation (衰减)

In physics, attenuation (in some contexts, extinction) is the gradual loss of flux intensity through a medium. For instance, dark glasses attenuate sunlight, lead attenuates X-rays, and water and air attenuate both light and sound at variable attenuation rates.

Hearing protectors help reduce acoustic flux from flowing into the ears. This phenomenon is called acoustic attenuation and is measured in decibels (dBs).

Attenuation decreases the intensity of electromagnetic radiation due to absorption or scattering of photons. Attenuation does not include the decrease in intensity due to inverse-square law geometric spreading. Therefore, calculation of the total change in intensity involves both the inverse-square law and an estimation of attenuation over the path.

The primary causes of attenuation in matter are the photoelectric effect, compton scattering, and, for photon energies of above 1.022 MeV, pair production.

Inverse-square law

Beer–Lambert law

Maxwell’s equations

Coulomb’s law

Ohm’s law

  • current-voltage relationship: V=IR
  • units of Resistance: ohms (Ω)

Ohm’s law formula relates only to substances that are able to induce power. such as metals and ceramic. However, there are many other materials for which the Ohm’s law formula cannot be used, such as semiconductors and insulators.

Joule heating

the power of heating generated by an electrical conductor equals the product of its resistance and the square of the current.

Electric power (电功率)

  • DC Electric Power: P = VI
  • E = V × I × T

Battery Capacity

Battery capacity (AH) is defined as a product of the current that is drawn from the battery while the battery is able to supply the load until its voltage is dropped to lower than a certain value for each cell.

参考

Physicist

Albert Einstein (1879-1955)

1933年回到美国后，爱因斯坦成为普林斯顿高等研究院的常驻教授，他此后有生之年，几乎都在这里度过，他再也没有踏上欧洲一步