Glossary of Physics (Z)

Zeeman Effect: The splitting of the spectral lines in a spectrum when the source is exposed to a magnetic field.
Zeroth law of thermodynamics: If body A is in thermal equilibrium with body B, and B is also in thermal equilibrium with C, then A is necessarily in thermal equilibrium with C.

Glossary of Physics (V)

Van der Wall's force: General term for weak attractive intermolecular forces
Vector Quantity: A quantity, which needs both magnitude and direction to describe it.
Velocity: Distance traveled by a body in a particular direction per unit time or the displacement of the body per unit time. It is a vector quantity.
Vibration: A back and forth motion that repeats itself.
Virtual image: An image formed when the reflected or refracted light rays appear to meet; this image cannot be projected on a screen.
Volt: Unit of potential difference, equivalent to joule/coulomb.
Voltage drop: The electric potential difference across a resistor or other part of a circuit that consumes power.

Glossary of Physics (U)

Ultrasonic Sound: Sound waves of frequencies above 20,000Hz.
Uniform Circular Motion: The motion of an object in a circular path with uniform speed.
Unpolarized light: Light consisting of transverse waves vibrating in all possible random directions.

Glossary of Physics (T)

Tesla: The S.I. unit of magnetic flux density, defined as the magnetic flux density of a magnetic flux of 1 Wb through an area of 1m2.
Thermal Capacity: The quantity of heat required to raise the temperature of the whole body by 1 .
Thermal Equilibrium: When the two bodies in contact are at the same temperature and there is no flow of heat between them, these are said to be in thermal equilibrium.
Thermal Expansion: The increase in the size of an object on heating.
Total internal reflection: Condition where all light is reflected back from a boundary between materials; occurs when light travels from denser to rarer medium and angle of incidence is greater than the critical angle.
Transverse wave: A wave in which the particles of the medium oscillate in a direction perpendicular of the direction of propagation of wave.
Trough: The point of maximum negative displacement on a transverse wave.

Glossary of Physics (S)

Saturated air: Air in which equilibrium exists between evaporation and condensation; the relative humidity is 100 percent.
Scalar Quantity: A physical quantity, which is described completely by its magnitude.
Second's Pendulum: A simple pendulum whose time period on the surface of earth is 2 seconds.
Semiconductors: Elements whose electrical conductivity is intermediate between that of a conductor and an insulator.
Shear strain: The ratio of the relative displacements of one plane to its distance from the fixed plane.
Shear stress: The restoring force developed per unit area when deforming force acts tangentially to the surface of body producing change in the shape of the body without any change in volume.
Siemens: The derived S.I. unit of electrical conductance, equal to the conductance of an element that has a resistance of 1 ohm, also written as ohm-1.
Simple harmonic motion: The vibratory motion that occurs when the restoring force is proportional to the displacement from mean position and is directed opposite to the displacement.
Snell's law: The ratio of sin i to sin r is a constant and is equal to the refractive index of the second medium with respect to the first.
Solenoid: A cylindrical coil of wire that becomes electromagnetic when a current flows through it
Sonic boom: Sound waves that pile up into a shock wave when a source is traveling at or faster than the speed of sound.
Specific heat: The amount of heat energy required to increase the temperature of one gram of a substance by 1 .
Speed: The distance traveled by a body per unit of time.
Spin quantum number: From quantum mechanics model of the atom, one of four descriptions of the energy state of an electron wave; this quantum number describes the spin orientation of an electron relative to an external magnetic field.
Standing waves: The waves formed due to superposition of two waves of same frequency and traveling in opposite directions with same speed.
Steam-point: It is the temperature of steam over pure boiling water under 1 atm pressure. It is equal to 100 or 212 .
Stefan-Boltzmann law: The amount of energy radiated per second per unit area of a perfectly black body is directly proportional to the fourth power of the absolute temperature of the surface of the body.
Superconductors: Some materials in which, under certain conditions, the electrical resistance approaches zero.
Surface tension: The property of a liquid due to which its surface behaves like a stretched membrane.

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.

Glossary of Physics (Q)

Quanta: Fixed amounts; usually referring to fixed amounts of energy absorbed or emitted by matter.
Quantum limit: The shortest wavelength, present in a continuous x-ray spectrum.
Quantum mechanics: Model of the atom based on the wave nature of subatomic particles, the mechanics of electron waves; also called wave mechanics.
Quantum numbers: Numbers that describe energy states of an electron.
Quark: One of the hypothetical basic particles, having charges whose magnitudes are one-third or two-third of the charge on an electron.
Q unit: A unit of energy, used in measuring the heat energy of fuel reserves, equal to 1018 British thermal units, or approximately 1.055x1021 joules.