Showing posts with label capacitor. Show all posts
Showing posts with label capacitor. Show all posts

PHYSICS DICTIONARY

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Capacitance

It is the ability of dielectric material between conductors to store charge, when a difference of potential exists between the conductors.


Capacitor

Passive device designed to store electrical charge. It is an arrangement of two conductors separated by dielectric.


Capillarity

The phenomenon of rise or fall of liquid in a capillary tube is known as capillarity.


Capillary Tube

It is a very thin tube made of rigid material such as plastic or glass. The tube is used to collect samples of liquids which flow into tubes against effects of gravity in a physical process called capillary action. The process uses two physical forces; “Surface Tension” and “adhesion”.


Carat

It is a unit used for measure of proportion of gold in an alloy, expressed as number of parts of gold in 24 parts of alloy. At present, 1 carat =200 mgm.


Carbon-Nitrogen Cycle:

A chain of thermonuclear reactions in which Nitrogen isotopes are formed in intermediate stages and Carbon acts essentially as a catalyst to convert four Hydrogen atoms into one Helium atom with the emission of two positrons is called as Carbon-Nitrogen cycle. The entire sequence is thought to generate significant amount of energy in the sun and certain other stars.


Carburizing

It is a process by which surface Carbon concentration of a ferrous alloy is increased by diffusion from surrounding environment.


Cardinal points

Points of an optical system, if known, the image would be determined easily without knowing the details of structure of system. Cardinal points constitute two principal points, two focal points and two nodal points.


Carnot’s Engine

Theoretical ideal engine, the concept of which is proposed by Sadi Carnot in 1824. As per this concept, there is no loss of heat due to friction etc and working substance is perfect gas. The engine is reversible and its efficiency depends only on temperature of source and sink, between which it works. No engine in practice can have efficiency more than it.


Carnot’s Cycle

Heat engine cycle concept proposed by Nicolas Sadi Carnot in 1823. It is the most efficient heat engine cycle consisting of two isothermal and two adiabatic processes. It is a reversible cycle involving no change in entropy i.e. it is an ideal concept in which total heat supplied is converted to work.


Carnot’s Theorem

Carnot’s theorem states that “working between the two given temperatures, no engine can be more efficient than a reversible Carnot engine. In other words, efficiency of a reversible engine is greater for two given temperatures than any other engine. 


Carrier Wave

Wave which carries information from transmission station and receiving station.


Cartesian Coordinates

Cartesian coordinates are rectilinear two dimensional or three dimensional, which are also called rectangular coordinates. The 3 axes of 3 dimensional Cartesian coordinates conventionally denoted by X, Y & Z axes are chosen to be linear and mutually perpendicular. In 3 dimensions, the coordinates X, Y & Z may lie anywhere in interval (-∞ & +∞ ).


Cathetometer

It is an instrument for the accurate measurement of small difference of height; especially of the differences in the height of upper surfaces of two columns of mercury or other fluid, or of the same column at different times. It consists of a telescope leveling apparatus which sides up or down a perpendicular metallic stand very finely graduated. The telescope is raised or depressed in order to sight the objects or surfaces, and the differences in vertical height are known.   


Cathode Ray Oscilloscope

It is an electronic display unit, first developed by German Physicist Ferdinand Braun in 1897. It contains a cathode ray tube that generates an electron beam that is used to produce visible patterns, or graphs, on a phosphorescent screen. The graphs plot the relationships between two or more variables, with horizontal axis normally being a function of time and vertical axis usually function of voltage generated by input signal to the oscilloscope. It is widely used test instrument for commercial engineering & scientific applications comprising acoustic research, television production engineering and electronics design.   


Cathode Ray Tube

An arrangement of vacuum tube equipped with electron gun which emits electrons. The electrons are accelerated and made to pass through electromagnetic field which gets deflected and falls on to fluorescent screen to form images.


Cathode Rays

Electron beam in vacuum tubes is referred to as cathode rays. They were first observed by German physicist Johann Hittorf and were named in 1876 by Goldstein.


Cathode

It is the electrode in an electrochemical or galvanic couple at which a reduction reaction occurs; thus the electrode that receives electrons from an external circuit is called as cathode. 

MICA CAPACITORS

Mica is popularly known as Isin glass. Important characteristics of Mica:

i) Its ability to operate at very high temperature (upto 500 oC).
ii) The material is almost totally inert and will not change with age, either chemically or physically.
iii) Mica is usable as a dielectric in its naturally state.
iv) It can be readily split into very thin sheets.

Mica capacitors are made by a method of depositing a thin layer of silver on each side of sheet of Mica was developed. This is done by a type of silver screen process. The silver is then fired in a furnace.

The principal advantage of Mica capacitor is its excellent degree of stability over a wide range of operating temperatures.

Mica capacitors are also among the best types to use where radio frequencies are involved.

Disadvantages of Mica capacitors:

i) They are relatively bulky when compared to other capacitors on a pure capacitance vs volume basis.


ii) The flat plates and method of construction lead to resonant frequency problems in some circuits.

Checking capacitors with an ohmmeter

Set the range of Ohm meter to higher range greater than 1MOhm. The ohm-meter leads are to be connected across leads of capacitor. Fora good capacitor, the meter first shows low value and then slowly recedes to a higher value. The reading gets stabilized to  a higher value after some time due to charging action.

For ceramic, paper and Mica capacitors, the resistance falls in the range 500 - 1000 MOhm.
For electrolytic capacitors, it is around 1MOhm.

If ohmmeter reading immediately goes to zero and stays there, the capacitor is short circuited.

If capacitor shows no charging action but just reads very high resistance it may be open.

Stray capacitance:

The wiring and components in a circuit have capacitance to metal chassis. The stray capacitance is typically 5 to 10PF.  

Leakage resistance of capacitor: 

Consider a capacitor charged by a DC voltage source. If the source is removed a perfect capacitor would keep its charge indefinitely.