Today in our 5th Science and
Technology class we revised few concepts in physics and some basic concepts in
chemistry.
Electricity:
Electricity is produced due
to movement of electrons its unit is coulomb
1
coulomb=6*10^18 electrons
Electric current:
Its SI unit is ampere
1 ampere = 1 coulomb/1 sec
Voltage:
In
simple terms it can be defined as the pull required to transfer electric
current from one point to another.
Resistance:
It
is the opposition of a material to the flow of current through it. Based on the
resistance value of a material it can be termed as conductor, semiconductor,
insulator and super conductor.
Factors influencing resistance:
(1)Length of the material:
Greater
the length, Greater the resistance.
(2Area of cross section:
Greater
the area of cross section, Lesser the resistance.
(3)Nature of the material:
As
we already know conductors have very low resistance, semi-conductors have
medium resistance and insulators have high resistance.
Magnetism:
It is the magnetic strength or magnetic
ability of a material.
Motor
creates magnetic energy by utilizing electric power
Generator
can be AC generator or DC generator it creates electric power by using magnetic
power.
AC and DC current:
AC
current is alternating in nature and DC current is non-alternating
Wastage
is very less in AC current and it is generally used for long distance power transmission
while DC is generally used for small distance power transmission.
CHEMISTRY
Two important laws of chemistry:
(1)Law of conservation of mass:
Mass
can neither be created nor destroyed in a chemical reaction.
(2)Law of constant proportion:
In
a chemical substance the elements are always present in definite proportion by
mass.
Atom and molecule:
Atom has a nucleus with photons,
electrons and neutrons .Molecule is formed by the connection of two or more
atoms.
Atom
is the smallest unit of element while molecule is the smallest unit of element
capable of independent existence.
Combustion:
Combustion
is the burning of carbon compounds which generally produces CO or CO2 as end
products. There are two types of combustion;
(1)Incomplete
combustion:
When
the combustion is stopped at the stage where CO is obtained as end product it
is called incomplete combustion.
(2)Complete
combustion
After
incomplete combustion if the process is carried out further by providing oxygen
supply it is called complete combustion. Its end product is generally CO2.
Fire triangle:
It
represents the three essential factors required for any combustion reaction to
take place.
(ie) Ignition temperature, fuel and oxygen
supply.
All these concepts provide a base for
understanding further concepts and in solving questions from these concepts.
