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Online Physics Glossary / Terms / Dictionary

Physics Definitions Start from D

Density - The amount of mass or number of particles per unit volume. In cgs units mass density has units of gm cm-3. Number density has units cm-3 (particles per cubic centimeter).

De Broglie Wavelength - Length of de Broglie wave of particle; Planck’s constant divided by momentum of particle.

Decibel - Unit of sound level.

Dependent Variable - Variable that responds to change in manipulated variable.

Derived Units - Unit of quantity that consists of combination of fundamental units.

Destructive Interference - Superposition of waves resulting in a combined wave with zero amplitude.

Diffraction - Bending of waves around object in their path.

Diffraction Grating - Material containing many parallel lines very closely spaced that produces a light spectrum by interference.

Diffuse Reflection - Reflection of light into many directions by rough object.

Dimensional Analysis - Checking a derived equation by making sure dimensions are the same on both sides.

Diode - Electrical device permitting only one way current flow.

Dispersion of Light - Variation with wavelength of speed of light through matter resulting in separation of light into spectrum.

Displacement - Change in position. A vector quantity.

Dissonance - Two or more sounds that, when together, sound unpleasant.

Distance - Separation between two points. A scalar quantity.

Diverging Lens - Lens that causes light rays to spread apart or diverge; usually a concave lens.

Dopants - Small quantities of material added to semiconductor to increase electrical conduction.

Doppler Shift - Change in wavelength due to relative motion of source and detector.

Dynamics - Study of motion of particles acted on by forces.

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