Electromotive force Definition
It is a unit measurement of energy that causes current to flow through a circuit. It is generally abbreviated as EMF. An electric current arises only when there is a difference in potential, called voltage. EMF can either be generated by an electrochemical cell or a magnetic field. The energy per unit charge is normally denoted by the symbol ε. An electric potential difference results when the positive and negative charges are separated. Attachment of a circuit to the source of EMF causes a current flow. There is a sudden dip in the voltage due to internal resistance that develops within the EMF source. Continue reading
Beam expander Definition
It is a combination of optical devices used to enhance the diameter of a laser beam or other light beams. In laser physics, the equipment functions either as an intracavity or extracavity element. It is more often denoted as “laser beam expander”. The low-cost optical instrument provides a high degree of accuracy. Continue reading
Negative resistance Definition
It is a characteristic of some electronic instruments in which an increase in the current (I) gives rise to a voltage (V) drop across the circuit. It is also called negative differential resistance or negative differential conductance. Normally in ohmic resistors, the current through a conductor between two points is directly proportional to the potential difference, according to Ohm’s law. On the other hand, negative resistors exhibit reverse behavior. Although it has only a theoretical existence, certain types of diodes display this property. It is analogous to negative temperature coefficient of resistance that occurs when a physical property of a material lowers with increasing temperature. Continue reading
This is an electromagnetic radiation generated when a charged particle such as an electron or a proton passes through a dielectric medium at a speed greater than the phase velocity of light. Dielectric is a poor conductor of electricity and hence, acts as an electric insulator, which gets easily polarized by these charged particles. Molecules of this medium return to the ground state, emitting radiation. Nuclear reactors, displaying blue glow is a phenomenon of the Cherenkov radiation. Continue reading
It is the property exhibited by some gels or fluids that are generally viscous or thick under normal conditions, but turn to a less viscous state when shaken, stirred or agitated. These gels later take a certain period of time to return to their original state when allowed to stand without being disturbed.
Viscosity of a non-Newtonian pseudoplastic fluid is inversely proportional to time; longer the fluid is prone to shear stress, lower its viscosity. The fluids have flow properties that are not described by a single constant value viscosity. These are dependent only on the shear rate. Thixotropic fluids generally take a specific amount of time to attain equilibrium viscosity when the value of the shear rate changes. The term “thixotropy” is derived from the Greek word “thixis” that refers to touch and “tropy” meaning, of turning, or to turn. Continue reading
It is the ability to reflect or bounce high-frequency waves and produce echo. It is greater when the surface or medium responsible for causing this phenomenon reflects increased sound waves. Continue reading
Lunitidal interval Definition
It is the mean time interval between the transit of the moon over the local meridian and the next high or low tide. Tides are periodic rises as well as falls of ocean water that are caused by the gravitational interaction between the Earth and the Moon.
It generally gives the time difference between two natural events that occurs simultaneously. The first event is when the moon passes over a meridian. The second event happens when the corresponding water tide reaches its highest peak. Practically, these two events do not take place simultaneously due to certain geographical features and disturbances. This in turn causes a time lag or interval between the transit of the moon and when the tide attains the highest level. It is also known as high water interval (HWI).
Bravais lattice Definition
It is a distinct lattice that normally repeats in order to fill the whole space. In mathematics, a lattice is a regular, geometric arrangement of points, particles, or objects throughout an area or a space, especially the arrangement of ions or molecules in a crystalline solid. A Bravais lattice is generally any of the 14 possible three-dimensional configurations of points that describe the orderly arrangement of atoms in a crystal. It can be generated by three unit vectors, a1, a2 and a3 and a set of integers that are denoted as n1, n2 and n3. In this way, each lattice point is identified by a vector R to obtain: Continue reading
Azimuthal quantum number is a quantum number or integer assigned to an atomic orbital. It is also denoted as “orbital angular momentum quantum number” or “second quantum number” and is designated by the symbol “ɩ”. It helps in the determination of the orbital angular momentum, which further helps in elucidating the shape of the electron’s orbital. Each electron has a set of four numbers, called as quantum numbers that is highly specific, and no two electrons in the same atom can have the same set of four quantum numbers. These constant numbers are essential to describe the position, spin, energy and orientation of an orbital in space. Continue reading
It is the broadening of the spectral line due to Doppler Effect of the random thermal motion of the molecules. Doppler effect is the change in the frequency of a wave for an observer moving relative to the source of the wave. Spectral line is basically an isolated bright or dark line in the spectrum (portion of the electromagnetic spectrum that is visible by the human eye) produced by emission or absorption of light of a single wavelength. Continue reading