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. 

ABOUT ELECTROLYTIC CAPACITORS

They provide more capacitance for their size than any other type. Electrolytics all have one thing in common, instead of usual plates separated by a dielectric, the electrolytic capacitor has a metallic anode coated with an oxide film. This outer covering is the dielectric, and a liquid electrolyte acts as a cathode. A second metallic conductor serves primarily as the connection to the liquid cathode, providing an external termination.

In actual practice, porous paper is wrapped around the anode and saturated with the electrolyte to eliminate the spillage problem.

There are two common types of electrolytic capacitors: a)  Aluminum  b) Tantalum

Both employ the same basic principle. The aluminum or Tantalum anode is covered with an oxide film. A suitable liquid or solid electrolyte is the cathode. The Aluminum type is by far the most popular because of its lower cost. The aluminum –oxide film has a very high resistance to current in one direction and has very low resistance to current in opposite direction. In other words, film acts as a dielectric in first instance and as a plate in second case. Because of this electrolytic are polarized. If the designated polarity is not observed, the oxide film on anode will breakdown and migrate to cathode connection, resulting in prompt failure of capacitor.

Electrolytics are described as belonging to one of the three basic families;

Polarized type

This type has one anode, the liquid cathode and a cathode connection. Polarity must be observed.

Semi polarized type

In many energy storage applications a certain amount of current reversal is often encountered. In such cases this type is recommended. In this type, the primary anode has a relatively thick oxide surface. The cathode connection now becomes the secondary anode with a thin oxide surface. Also liquid cathode has a slightly different chemical composition.

Non-polarized

This type is used in audio cross over networks and ac motor starting applications. Here there is a complete reversal of polarity; therefore, two anodes are required. The cathode connection now becomes a second, and equal, anode. Obviously size will be affected. Infact, the third type called nonpolarized is just twice as large as a polarized type of equivalent capacitance and voltage rating.

Small trick for designers using capacitors

Suppose you require a smaller capacitance with higher voltage rating for your application but you are left with only higher capacitance capacitor with less voltage rating. How could you overcome this problem?

You can follow a small trick. You put two or more capacitors in series to arrive at your designed capacitance of smaller value.Because
i) It divides the voltage over two capacitors and thus has net effect of doubling (in case of two capacitors) the voltage rating.
ii) It reduces overall capacitance by following

C = (C1*C2) / (C1+C2 )

where 'C' is total capacitance of two capacitors in series.

For instance, consider two capacitors 100 pF @500VDC,

Then keeping them in series we get C = 50pF

voltage is now divided over two capacitors so total rating is 50pF @1000V Dc.

Hope this is helpful for designers.