أكاديميا - كولنز - معاجم الجيب العلمية - الفيزياء - انكليزي - فرنسي - عربي الحرف ٢_ d

Academia - Collins - Pocket Scientific Dictionaries - Physics - English - French - Arabic Letter 2_ D


diffraction
difference f

Diffraction. Bending of a wave around the edge of a dark particle within a shaded region. It is easy to see diffraction in water waves in ports and in the ripple tank. The figure below shows typical diffraction results.

All waves can bend around suitable bodies. The effect will not be significant unless the size of the body is close to the wavelength of the waves.

Light is deflected by a narrow slit to produce a group of interference fringes. The hair shadow shows overlapping at the edges and a bright line in the middle.

Because diffraction depends on the wavelength, it may lead to dispersion, and the diffraction grating - diff fraction grating is a useful source of spectra. Each wavelength can move in only a few directions due to interference.


diffuse reflection
Reflection f diffuse

Diffuse reflection. Reflection by a rough surface, such as the paper of this book and most objects we see. A flat, smooth surface reflects a parallel beam as a parallel beam, while a rough surface does not do this and therefore cannot produce images. However, it is all subject to the laws of reflection.


diffusion
diffusion f

All scattering. The way in which particles of a fluid released from a source spread through an available vacuum. Thus, people around the room quickly smell gas coming from one of its corners. Liquids do not scatter at the same speed as gases because their particles move at lower speeds and collide frequently with each other.

Scattering forms part of the evidence for the kinetic model of matter.


digital system
System number

Digital system. A system that uses numbers from 0 to 9
(decimal system) to display a reading instead of a scale, as in a thermometer or the pointer of a measuring device, which is called an analogne system. The system with two numbers is called a binary system.


diode
diode f

bilateral . A two-mode device is mainly used as a rectifier. Older types include the valve diode, the point-contact diode (cat's whisker), and the p-p-n junction, which is the modern type of semiconductor, and can replace other types in almost all cases.

The cat's whisker diode involved a thin metal wire (the hair) pressed against a crystal surface, and served as the first stage after the antenna in early crystal radios. Its mission was to straighten the signal coming from the antenna to allow the auditory part to be obtained. Modern demodulator circuits do the same thing.


dioptre(D)
dioptre m

A broken one. A unit of power of a lens, mirror, or system for deflecting light. The power of the lens, mirror, or system is the reciprocal of the focal distance in meters. Thus, a 5-fractal lens has a focal length of 200 mm.

1/0.2 = 5

direct current (DC)
Courant m continu

Continuous current. Charge flows in only one direction.
Compare with alternating current. In most cases we also expect the current to be reasonably constant. Thus, the current shown in the drawing below is treated as a direct current with an alternating current ripple.