current and electricity

Monday, May 1, 2023IMRAN 1

CURRENT ELECTRICITYIntroduction:-The branch of physics which deals

with the motion of charges is called current electricity. Since the electronic current in a conductor is due to the motion of free electrons therefore these electrons are also known as conduction electron. The flow of free charges in a conductor constitutes electric current.

Electric current:- It is defined as the charge flowing through any section of conductor in one second.


I = q / t AmperesThe SI unit of electric current is ampere (A).The current flowing in a conductor is said to be one ampere if one coulomb of charge flows across any of its cross-section in one second. i.e., 1 ampere = (1 coulomb)/(1 second)Electric current is macroscopic and scalar quantity.Steady current is that current which does not vary

with time. Varying current is a current whose magnitude varies with time.


An alternating current is a current whose magnitude changes continuously with time and direction changes periodically.

The electric current is generally measured by its magnetic effect, chemical effect, heating effect etc.

Battery:- It is generally made up of a number of electrochemical cells connected in series. The chemical energy stored in these cells is converted into electrical energy.

Dynamo:- In a dynamo (or generator), it is the mechanical energy which is converted into electrical energy.


Battery eliminator:- In this device, the alternating current of the electric mains is converted into direct current.

CLASSIFICATION OF MATERIALS IN TERMS OF CONDUCTIVITY:

Conductors:- The materials whose electrical conductivity is very high are called conductors. Such as earth, human body, aqueous solutions of salts, copper, iron, brass, aluminium etc.

Insulators:- The materials whose electrical conductivity is very very small are called insulators. Such as quartz, glass, dry air, wood etc.


Semiconductors:- The materials whose conductivity lies between that of conductors and insulators are called semiconductors. Such as germanium, silicon.


Current density:- The electric current at a point,

within a conductor, is the current through a unit area of the conductor, around that point, provided the area is perpendicular to the direction of flow of current at that point.

Electric current density is a vector whose direction is the same as the direction of flow of current.


DIFFERENCE BETWEEN CURRENT &

CURRENT DENSITY:-

Current density CurrentIt is a characteristic of some point in a conductor.

It is a characteristic of the whole of the conductor.

It is a microscopic quantity.

It is a macroscopic quantity.

It is a vector quantity. It is a scalar quantity.


Electrical resistance:- The resistance of conductor

is the opposition offered by the conductor to the flow of electric current through it.

The SI unit of resistance is ohm.The resistance of a conductor is said to be one

ohm if a current of one ampere flows through the conductor when a potential difference of one volt is applied across its ends.


Resistivity (specific resistance):- The resistivity of a

material is the resistance of a conductor of this material of unit length and unit cross-sectional area.

Resistors:- Resistors can be carbon resistors or wire-wound resistors. Both the types can either have a fixed or a variable value. To make a carbon resistor of fixed value, carbon with a suitable binding material is moulded into a cylinder. Wire leads are attached to this cylinder. The resistor is encased in a plastic or ceramic jacket. The resistor is connected to the circuit by means of two leads.


COLOUR CODE FOR CARBON RESISTANCE:Letter as an aid to memory

Colour Number Multiplier

B Black 0

B Brown 1

R Red 2

O Orange 3

Y Yellow 4

G Green 5

B Blue 6

V Violet 7

G Grey 8

W White 9

Colour Tolerance

Gold

Silver 10%

No colour 20%


Aid to memory. B.B. Roy Great Britain Very Good Wife. The bold faced letters correspond to colours in the correct sequence.

Another mnemonic device used to remember this code is “Bad Bees Ravage Our Yellow Geraniums But Violets Grow Wildly.”

current and electricity

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