أكاديميا - كولنز - معاجم الجيب العلمية - الفيزياء - انكليزي - فرنسي - عربي الحرف ١_ d

Academia - Collins - Pocket Scientific Dictionaries - Physics - English - French - Arabic Letter 1_ D


decay
desintegration f

Decay. In physics, the decay of a measure describes how its size shrinks over time. As for radioactivity, it describes how activity changes over time.

Both concepts share the diagram below. The measurement on the y-axis (y) may be the number of active nuclei in a sample, the charging current in a capacitor, or the amplitude of the vibration of a damper.

This graph shows an exponential decay, as any value of (y) halves within a certain period of time. Look . half-life period


demagnetization
démagnétisation f

Demagnetization. A magnet can lose its magnetic strength when treated roughly or when stored without magnet keepers. To completely demagnetize a sample, it must be pulled slowly to a distance of a meter or so from a solenoid coil of strong alternating current and moved along the axis of the coil.


density(D)
density f

Density. The density of a substance is the mass of any sample divided by its volume, and its unit in the International System of Units (SI) is the kilogram per cubic meter. We often use the gram per cubic centimeter.

Density D = mass m / volume 7

The density of water is 1000 kg/m (or 1 g/cm).

It is often more useful to use relative density, which is the density of the substance Ds divided by the density of water, i.e. RD = DDW. This density has no unity.

The density of iron is 7900 kg, so its relative density is 7.9.

Since the volumes of solids and liquids change only slightly with changes in temperature and pressure, the densities of substances remain constant. On the other hand, the density of gases changes greatly with changes in temperature and pressure.
See also optical density.

detection of radiation
detection of radiation

Radiation detection. Nuclear radiation can be detected by a Geiger-Miller tube or by a cloud chamber. The method of detecting electromagnetic radiations depends on the type of these radiations.

For example, it is possible to detect


deuterium
deuterium m

Deuterium. The isotope of hydrogen, which has a nucleon number of 2 instead of the normal value of 1. The nucleus of deuterium (deuteron) is a neutron in addition to a hydrogen proton. Thus, the density of deuterium is twice that of ordinary hydrogen, but many of their physical properties are not similar because they depend on density. Deuterium is often called “heavy hydrogen.”

Heavy water is deuterium oxide D20. Its melting temperature is 4°C and its boiling temperature is 102°C. Its density is 10% higher than the density of water, H₂O.


dielectric
dielectrique m

Permeable electricity. A substance that polarizes in an electric field and remains charged when the field disappears. Electroconductive materials are used to make electrolytes, which have two oppositely charged sides. Compare with magnet.

Good insulators of this type are used between capacitor plates. The “relative permittivity” (rela tive permittivity) and “dielectric constant” measure its values ​​in this context.

The drawing below shows how particles of a non-polarized substance (A) differ from particles of a polarized substance (B). See also piezo - electricity.