Electricity
CHARGE
Charge is an intrinsic property of matter by virtue of which
it can exert electromagnetic force, i.e. attraction between
the unlike charges or, repulsion between the like charges.
Unit of charge: coulomb (C)
Like Charges Unlike Charges
Force of Repulsion Force of Attraction
ELECTRIC CURRENT ()
Amount of charge flowing through a particular area in unit
time.
Current ( = Charge ()
Time (s)
Unit of current: ampere (A)
One ampere is constituted by the flow of one coulomb of
charge per second, that is, 1 A =
1s
The direction of electric current is taken as opposite to the
direction of the flow of electrons, which are negative charges.
Electric Circuit and Circuit Diagram:
. A closed-loop path which a current takes is called an electric
circuit.
Bulb Switch
Connecting
Battery Wire
Electric Circuit (Vedantu)
O-SWITCH COPEN) - LAMP
o - swITCH (CLOSE FUSE
vOLTMETER
BATTERY -A AMMETER
Electric Components & Symbols
ELECTRIC POTENTIAL AND POTENTIAL DIFFERENCE
The electric potential at a point is defined as work done
in bringinga unit positive charge from infinity to that
point.
The potential difference is defined as the work done to
move a unit charge from one point to another.
Potential difference (V) = Work (W)
Charge (Q)
Unit of potential difference is volt.
Potential difference is 1 volt when 1 joule of work is
done to move 1 coulomb of charge from one point to
another.
OHM'S LAW
The potential difference across the ends of a given metallic wire
in an electric circuit is directly proportional to the current flowing
through it, provided its temperature remains the same.
Current (A)
V =IR
Voltoge (V) Resstance (0)
V wR RY
Ohm's Law
(Nedantiu
RESISTANCE
The property of a conductor to oppose the flow of charges
through it.
.Sl unit of Resistance is ohm (Q).
One ohm is the resistance offered by a wire carrying one
ampere current when one volt of potential difference is
applied across its ends.
1V
R= 10=4
1A
Factors affecting Resistance
Resistance is
.directly proportional to the length () ofthe conductor.
directly proportional to the nature of material ofthe
conductor (p.
.inversely proportional to the cross-sectional area (A) of
the conductor.
.depends on the temperature of the conductor.
RP
Resistivity (P)
The electrical resistance offered bya substance of unit
length and unit cross-sectional area is called resistivity or
specific resistance.
RA
Resistivity(P) =
Sl unit of resistivity: ohm-meter(0 m)
Conductivity(o)
The degree to which a specified material conducts
electricity. Conductivity is reciprocal of resistivity.
Conductivity(o) =
*p ;RA
=
SI Unit of Conductivity: (ohm m') or (mho - m)
(Vedant)
Classifcation of Materials based on Resistivity:
Conductors Semi-
Insulators
conductors
Materials with the Materials with the Materials with
least resistivity to highest resistivity to resistivity ranging
the flow of the flow of between conductors
electricity. electricity. and insulators.
Ex: Iron, Silver, Ex: Glass, Wood, Ex: Silicon,
Copper etc. Plastic etc. Germanium etc.
Resistivity 1 0 to Resistivity- 1012 to Resistivity-10 to
10 Qm 101 Qm 105 Q m
Resistivity: Metals< Semiconductors< Insulators
Conductivity: Metals > Semiconductors> Insulators
Effect of Temperature on Resistivity
With increase in temperature, Resistivity of
Conductors Increase
Insulators Increase
Semiconductors Decrease
RESISTORS IN SERIES
In series combination, the sum of the individual resistances
of multiple resistors in series equals their equivalent
resistance.
W-WM
R Ra R
RtotalR+Rzt+R
****
Resistors in Series
Nedant
I n a series arrangement, current across the individual resistors
remains the same and potential differences vary.
RuoLAny of the individual resistance.
When n number of identical resistors are connected in series
then resultant resistance is Ro nR (Where Ris the resistance
of each resistor)
RESISTORS IN PARALLEL
In parallel combination, sum of the reciprocals of the individual
resistances is equal to the reciprocal of the equivalent
resistance of a group of resistances linked in parale!.
Resistors in Parallel
In parallel arrangement, potential difference across each
individual resistor remains the same but the current varies.
When n number of identical resistors are connected in parallel,
thenresultant resistance is Rotal R/n. (Where R is the
resistance of each resistor).
HEATING EFFECT OF ELECTRIC CURRENT
When electric current is passed through a conductor which
acts as a resistance wire, the resisting nature of the
conductor results in the rise in heat level of the conductor
with time. This phenomenon is the heating effect of the
electric current.
adant
Joule's Law of Heating
Heat produced (H)« square of the current ().
. H Resistance (R) of the given circuit.
H Time (t) for which current flows through the
conductor.
H= IRt
Electric Fuse
Electric fuse is a device which is used in series to limit
the current in an electric circuit so that, it melts easily due
to over heating when excessive current is passed through it.
Fuse wire is made ofa material with very low melting point.
For e.g. Alloys of Aluminum, Tin, Lead etc.
Electric Fuse
Electric Bulb
Filament of the bulb glows when heated because it is
incandescent.
Fllament
Electric Bulb
T h e filament is made thin and coiled, to increase resistance.
T h e filament needs to withstand high temperature, so it is
made of tungsten (Melting point: 3422 °C, 6192 °F).
Vedantiu)
ELECTRIC POWER
. The rate at which electric energy is dissipated or
consumed in an electric circuit is termed as Electric Power.
T h e power Pis given by
P=VI =PR =
.The SI unit of power is watt (W).
One watt of power is consumed when 1 A of current flows
at a potential difference of 1 V.
1 watt = 1 voltx 1 ampere
The commercial unit of electrical energy is a kilowatt-hour
(KWh).
. One kilowatt-hour is defined as the amount of energy
consumed when 1kw of power is used for 1 hour.
1 kWh 3.6 x 10° J.
GOOD LUCK
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