A B C D E F G H I J K L M N O P Q R S T U V W X Y Z


Radiation:
The emission and propagation of waves transmitting energy through space or through some medium.
 
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 law:
The rate of disintegration of a radioactive substance is directly proportional to the number of undecayed 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:
The natural spontaneous disintegration or decomposition of a nucleus.
 
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
 
Reverberation:
"The prolongation of sound at a given point after direct reception from the source has ceased
 
Rigid body:
An idealized extended body whose size and shape is fixed and remains unaltered when forces are applied.