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


discharge. discharge
charge f

evacuation . Transfer of charge from a charged body. We often use this word in special cases to discharge a chemical source or a capacitor, and to discharge a current into a gas or empty space. In the latter cases, a high voltage is needed to produce a spark (see lightning). See conduction, electrical.

Discharge tubes include “neon” and “fluorescent” lamps. These contain low-pressure gases, where a fairly low voltage creates a current with energy transferred into radiation. The radiation is often ultraviolet. To convert this into light, the LED (tube) is coated with a fluorescent powder.


dispersion
dispersion f

Distracted. When radiation is bent, as a result of refraction or diffraction, the angle of bending depends on the wavelength. For example: When white light passes at an angle from air to glass, blue rays are bent more than red ones. The white light is thus dispersed. See colour.


displacement
deplacement

Displacement is another word for “distance,” but it is actually a vector describing the change in position of an object. Its unit is the meter and its symbol is . Its numerical form is distance, indicated in the drawing below by the symbol A. If something moves from A to B and then to C, i.e. a distance of 7 km, a body will have a displacement of 5 km in a direction of 54°.

In wave movement, displacement measures the disturbance starting from zero at a specific point in a specific time. The largest value is the amplitude of the wave.


distance ratio
Rapport m de vitesses

Distance ratio. In a machine, the force involved causes movement and converts the energy into the movement of the load. The distance ratio (speed ratio) is the distance moved by the output power divided by the distance moved by the input at the same time. There is no unit for this ratio. See also efficiency. Also called velocity ratio.


domain. domain
domaine m

Square. A region in a magnetic material with a magnetic field. The particles form magnetic fields as a result of the flow of charge in their electronic clouds.

All particle fields in the field are in one direction.

The field fields in a non-magnetic sample (a) form closed loops, and this does not have any net effect. When the sample is magnetized, the fields change, giving the net effect shown in (b).

Doppler effect
effet m Doppler

Doppler effect. The apparent change in frequency of waves when the source moves relative to the observer. Thus, the police car siren has a higher pitch than normal as it approaches and a lower pitch as it moves away.

The red shift of light from stars is the same reason.


dynamics
dynamic f

Animation. Study of the movement of objects and the forces that cause changes in movement. See equations of motion. Newton's laws of force,


dynamo
dynamo m

Dynamo. See generator.