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Academia - Collins - Pocket Scientific Dictionaries - Physics - English - French - Arabic Letter 3_ P


phase
phase f

Develop . The state of a wave or vibration at a particular moment. Since all waves and vibrations can be represented by sine curves, the phase is the point on that curve at that moment.

The term phase difference is more commonly used than phase, which is the difference in phase between two waves that would have been the same at a given point if that difference had not existed. The two waves in Figure (A) below have a phase difference of 45°, while the two waves (B) are in an antiphase with an angle of 180°.


photo - cells
FPL photoelectric cells

Photocells. Devices that rely on photoelectric reactors, and here radiation energy is converted. photo - electric effects Energy is electrical charges, and this has three possible results:


photo - electric effects
effets mpl photoélectriques

Photoelectric effects. This is observed when the radiation energy absorbed by the material causes an electrical change. Energy separates electrical charges. This has three possible outcomes:

Photo-emission, which is the “evaporation” of electrons from the illuminated surface of the carrier.

A certain amount of energy, depending on the surface, is needed to make the electron escape. Therefore, the maximum energy of a photoelectron is equal to the energy of a photon of radiation minus the escape energy. The photon energy is directly proportional to the frequency. Therefore, every surface has a threshold frequency below which no light will be emitted, regardless of the intensity of the radiation.

Photo-conductivity, which appears in semiconductors. Its conductivity increases and its resistance decreases when it is lit. Radiation leads to “displacement” and ionization of atoms in the sample. The resulting electron-hole pairs allow a higher current to pass.

Photo-voltaic effect, which appears in semi-conductor connections, where radiation produces an electromotive force across the connection. This is also caused by displacement. Electrolytic solutions can also show the same effect.

physical change
change m physique

Physical change. A change in a system that one can simply reverse by reversing the relevant energy transfer. Examples are the fusion of solids and the fission of the nucleus. Also, chemical change can be reversed, but this task is not easy.
Thus, it is not difficult to convert a gas into a liquid and then turn it back into a gas, while it is difficult to reverse the combination of hydrogen and oxygen to form water.


physics
physical f

Physics. The study of matter and energy and how one affects the other. Therefore, physics is the broadest of all sciences, as it is the basis of chemistry, which in turn is the basis of biology, astronomy, geology, etc., and mathematics is its main tool.

In practice, people tend to divide physics into a number of fields, although this division is almost universal
Artificially. These basic fields are: waves, energy, thermal physics, mechanics, electricity, magnetism, quantum theory, and relativity.
Nuclear physics.

piezo - electricity
piézoélectricité f

Piezoelectric. Stress in some crystals causes a voltage between opposite faces. This effect has many uses, including strain gauges, pressure gas burners, and microphones. There is also a reverse effect for piezoelectricity. If an alternating voltage is applied, the crystal vibrates.


pitch. pitch
hauteur f

Pitch. It is in common sound the word
For a description of frequency see quality of sound.