Sunday, 8 December 2013

Glossary of Physics (R)

Radiant energy: The form of energy that can travel through space; for example, visible light and other parts of the electromagnetic spectrum.
Radiation: The emission and propagation of waves transmitting energy through space or through some medium.
Radioactive decay: The natural spontaneous disintegration or decomposition of a nucleus.
Radioactive decay constant: A specific constant for a particular isotope which is the ratio of the rate of nuclear disintegration per unit time to the total number of radioactive nuclei.
Radioactive decay series: Series of decay reactions that begin with one radioactive nucleus that decays to a second nucleus that decays to a third nucleus and so on until a stable nucleus is reached.
Radioactive decay law: The rate of disintegration of a radioactive substance is directly proportional to the number of undecayed nuclei.
Rarefaction: A part of a longitudinal wave in which the density of the particles of the medium is less than the normal density.
Real image: An image which can be projected on a screen.
Rectilinear Motion: The motion of a body in a straight line.
Reflection: The bouncing back of a wave from a boundary.
Refraction: The bending of light from its straight line path when it travels from one medium to another.
Refractive index: The ratio of speed of light in vacuum to that in the medium.
Relative density: The ratio of density of a substance to the density of water at 4 .
Relative humidity: The percentage of the amount of water vapor actually present in a certain volume of the air to the amount of water vapor needed to saturate it.
Resolving power: A quantitative measure of the ability of an optical instrument to produce separable images of different points of an object.
Resonance: When the frequency of an external force matches the natural frequency of the body then the body oscillates with large amplitude.
Restoring force: The force which tends to bring an oscillating body towards its mean position whenever it is displaced from the mean position.
Resultant Force: A single force, which acts on a body to produce the same effect in it as, done by all other forces collectively.
Reverberation: The prolongation of sound at a given point after direct reception from the source has ceased, it is due to reflections from the boundary surfaces.
Rigid body: An idealized extended body whose size and shape is fixed and remains unaltered when forces are applied.

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