Current
Electricity and Magnetism
Electric
Charge
·
It is something that a body attains when it
loses or gains the electrons.
·
The positive and negative labels and sign for
electric charges were chosen arbitrarily by Benjamin Franklin
·
Similar charges repel each other while opposite
charges attract each other.
·
Charge is a scalar quantity and its SI unit is
coulomb C.
·
Electricity is associated with the charge.
·
The proton possesses positive charge (+e) and
electron possesses an equal negative charge (-e), where, e=+1.6 x 10 -19 C
·
Conductors are those substances which allow
passage of electrical charge to flow through them and have very low electrical
resistance. ⚫ Metals like silver, iron, copper
are conductors.
·
Human body and Earth act like a conductor.
Silver is the best conductor .
·
Insulators
are those substance which do not allow passage of charge through themselves.
Rubber, wood, mica, glass, ebonite are insulators.
Electric
Current
Rate of flow of change is known as electric current. Its
unit is ampere. It is of two types.
(i) Alternating current (AC) (ii) Direct current
(DC)
Rectifier It is a
device used to comert A.C. into D.C.
Electric
Power
It is the electric work done by the electric instruments per
unit time, i.e.
P= 
Its
unit is watt.
Kilowatt
Hour (KWH)
·
It is the unit of energy and is equal to the
energy consumed in the rate of 1 kilowatt (1000 J/s) for 1 hour.
·
I kilowatt hour = 3.6x 10° joule.
Heating
Effect of Electric Current
·
Production of heat in an electric device due to
flow of electric current is called heating effect of electric current. An
electric bulb, electric fuse heater used food cooking or room heater, etc., are
the examples of heating effect of current.
·
Electric bulb is a device which converts electrical
energy into light and heat energy.
·
An electric bulb contains a tiny wire Inside the
glass cover which is called filament Filament is made up of tungsten.
·
An electric fuse is a device works on the
heating effect of current.
·
It prevents from electric fires or damage of
electrical appliances.
·
Electric fuse consists of a short length of a
thin wire (plated copper) and having low melting point and high resistance.
·
We should not use a thick wire as a fuse wire
because it will have a low resistance.
Chemical Effect of Current
·
When electric current is passed through
conducting liquids, then chemical changes takes place. This is called chemical effect of current cell.
·
Cell is an example of chemical effect of current
cell.
Cell
Cell converts chemical energy into electrical energy. These
are of two kinds
·
Primary
Cells In this type of cells. the chemical energy is converted into
electrical energy, but the chemical reactions occurring are irreversible.
·
Secondary
Cells Secondary cells are those cells in which it is possible to restore
electrical energy from the chemicals present in the cell.
Solar
Batteries (Solar Cells)
It is a technique in which solar energy is converted into
electric energy. It contains a slim rod of silicon covered with arsenic atom,
and a layer of boron and silicon When sunlight falls on it, a small potential
difference develops. This phenomena can be referred as photoelectric effect it
is used to give the power to the artificial satellites
Electroplating
In this process, a thin layer of a desired metal over
another metal is deposited with the help of electric current. It is called
electroplating
Current
Measuring Devices
Galvanometer
It is a device used to detect and measure electric current
in a circuit. It can measure current upto 10 -6 A
A galvanometer can be converted into a voltmeter by
connecting a very high resistance in its series.
§
Shunt is a low resistor connected in parallel
with a circuit or device that reduces the amount of electric current flowing through
it.
Ammeter
·
It is a device which is used to measure electric
current in a circuit.
·
It is a connected in series in the circuit.
·
The resistance of an ideal ammeter is zero.
Voltmeter
·
It is a device used to measure the potential
difference between two points in a circuit.
·
It is connected in parallel in the circuit.
·
The resistance of an ideal voltmeter is
infinite.
Transformer,
Motor and Dymano
·
It is a device which converts low voltage AC
into high voltage AC and high voltage C. It is based on electromagnetic
induction.
·
Step-up transformer converts a low voltage of
high current into a high voltage of low current. Step-down transformer converts
a high voltage of low current into a low voltage of high current.
·
DC motor is a device which converts electrical
energy into mechanical energy
AC Dynamo (or
generator) is a device used 10 convert mechanical energy into electrical
energy. It works on the principle of electro-magnetic induction.
Magnets
·
The material which can attract the magnetic
substances (such as cobalt, iron and nickel) is called a magnet and the
property of attracting the magnetic substance by a magnet is called magnetism.
·
The magnetism which do not lose their magnetism
with normal treatment are called permanent magnets.
·
The materials which retain their magnetism for a
long time are called hard magnetic materials. When a magnet is freely
suspended, it aligns itself in the geographical North-South direction.
·
The permanent magnets are made of certain alloys
of nickel, cobalt and alloys of iron with some carbon. They are made in various
shapes such as bar, rod, disc, ring, etc.
·
When poles of two magnets are brought close
together, they exert force on each other.
·
Similar poles repel each other and dissimilar
poles attract each other.
·
The area surrounding the magnet in which,
another magnet experience a force on it is called magnetic field.
The unit
of magnetic field is
newton/ampere- metre or
weber/metre² or tesla.
Electromagnets
·
An electromagnet is a solenoid coll that attains
magnetism due to flow of current.
·
It consists of a long insulated copper wire wound around a
soff-iron core.
·
The magnetic effect remains only till the
current is passing through it.
