Download Chapter-16 Electricity

Comprehensive Physics Notes
Class X
Chapter-16 Electricity
ABDUL RASHEED
Educast
Contents
Learning Objectives
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Electrical nature of matter
Insulators and conductors
Electric field
Electrostatic induction
Electrostatic potential
Capacitor
Electromotive force
Electric cells
Electric current
Electric circuit and combination of resistances
Direct and alternating current
Electrical energy and Joules law
Houses circuits
DEFINITIONS
COULOMB
It is SI unit of electric charge. One coulomb (1C) of charge being that quantity of
charge which when
placed one meter from an identical charge in vacuums repels it with
a force of 8.99 x 109 N.
INSULATORS
Insulators are those materials, which do not allow electric charges to pass through
them. In other words,
insulators are materials that do not allow electrical current to
pass. In insulators electrons are tightly
bounded to their atoms. Insulators do not have
free electrons.
Examples Plastic, rubber, wood, glass etc.
CONDUCTOR
Conductors are those materials, which allow electric charges to pass through them. In
other words,
conductors are materials that allow electric current to pass. In
conductors electrons are loosely bounded
to atoms. Conductors have free electrons.
Examples:
Copper, Gold, Aluminum, Silver etc.
ELECTRIC FIELD
Space or region surrounding a charge or charged body within which another charge
experiences some
electrostatic force of attraction or repulsion when placed at a point is
called Electric Field.
ELECTRIC INTENSITY
It is the strength of electric field at a point. Electric intensity at a point is defined as the
force
experienced per unit positive charge at a point placed in the electric field.
Mathematically,
E=F/q
It is a vector quantity. It has the same direction as that of force.
Units
N/C or Volt/m
E=1/4
ELECTRICAL
POTENTIAL
x
q/r2
Electric potential at a point is defined as the amount of work done in moving unit
positive charge against
the direction of electric field from a point to that point.
Electrical potential = work done/charge
or
U=work/q
unit of electric potential in SI system is Volt .
1 volt = 1 Joule/coulomb
VOLT
Unit of electric potential and potential difference in SI system is called Volt.
It is defined as
"in an electric field potential b/w two points is 1 volt if the amount of work
done in moving 1 Coulomb charge from one point to another point is 1 Joule."
POTENTIAL
DIFFERENCE
Potential difference b/w two points A and B is equal to the amount of work done by
moving a unit positive
charge from point A to point B against the electric field
VB-VA=VAB
or
VAB= (work)AB/q
Unit
Volt or Joule/Coulomb
ELECTRIC CURRENT
The rate of flow of electric charge through a cross section of a conductor is called
Electric Current or
Electric charge passes through a cross section of a conductor is
called Electric Current.
It is denoted by I.
FORMULA
I = Q/t
UNITS
Ampere in SI system.
OTHER UNITS
mA (milli Ampere) = 10-3A
 A (micro Ampere) = 10-6A
AMPERE
If one coulomb of electric charge passes through a cross section of a conductor in one
second, the
amount of current passes through it is called Ampere. 1A = 1c/1sec.
RESISTANCE
opposition offered by the atoms of a conductor in the flow of electric current is called
Resistance. It is a
hurdle in the flow of electric current. Different substances have
different resistance. Resistance of a
conductor increases with the increase in
temperature.
SYMBOL
It is denoted by R.
UNIT
Ohm
CAPACITOR
Capacitor is an electronic device, which is used to store electric charge or electrical
energy. A capacitor
stores electric charge on its plates. There are a number of types of
capacitors available.
STRUCTURE OF
CAPACITOR
A capacitor consists of two identical conducting plates which are placed in front of each
other. One
plate of capacitor is connected to the positive terminal of power supply
and the other plate is connected
to negative terminal. The plate, which is connected to
positive terminal acquired positive charge, and the
other plate connected to negative
terminal. Separation between the plates in very small. The space
between the plates is
field with air or any suitable dielectric material
A parallel plate capacitor
PRINCIPLE OF
CAPACITOR
Electric charge stored between the plates of a capacitor is directly proportional to the
potential
difference between the plates.
Let the potential difference between the plates is V and the charge stored on any one
of the plates of
capacitor is Q then,
QV
Q = CV
where
C= Capacitance of the capacitor
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CAPACITANCE
Charge storing capability of a capacitor is called capacitance of capacitor.
Definition: Capacitance of a capacitor is defined as the ratio of the charge stored on
any of the plates of
capacitor to the potential between the plates.
COMBINATION OF RESISTORS
.
Resistance can be joined to each other by two ways:
1. Series combination
2. Parallel combination
SERIES COMBINATION
Characteristics:
1. If different resistances are joined with each other such that there is only one path for
the flow of
electric current then the combination of such resistances is called Series
Combination.
2. In series combination current through each resistor is constant.
3. In series combination Potential difference across each resistor is different depending
upon the value of
resistance.
4. Equivalent resistance of circuit is equal to the sum of individual resistances.
Re = R1 + R2 + R3 + R4 + …………….. Rn
DISADVANTAGE
If one component is fused, then the other components of circuit will not function.
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EQUIVALENT
RESISTANCE IN SERIES
COMBINATION
Consider three resistances R1, R2, & R3 connected in series combination with a power
supply of voltage.
Potential difference of each resistor is V1, V2, & V3 respectively. Let electric current I is
passing through
the circuit.
Now
V = V1 + V2 + V3
According to Ohm’s law V = IR
thus
IRe = IR1 + IR2 + IR3
IRe = I(R1 + R2 + R3)
IRe/I = R1 + R2 + R3
Re = R1 + R2 + R3
This shows that in series combination equivalent resistance of circuit is always greater
than individual
resistances.
PARALLEL
COMBINATION
Characteristics:
1. If there are more than one path for the flow of current in a circuit then the
combination of resistances
is called Parallel Combination.
2. In parallel combination current through each resistor is different.
3. Potential difference across each resistor is constant.
4. Equivalent resistance of circuit is always less than either of the resistances included
in the circuit.
ADVANTAGE
In parallel combination of resistors, if one component of circuit (resistor) is damaged
then rest of the
component of the circuit will perform their work without any
disturbance. It is due to the presence of
more than paths for the flow of electric
current.
EQUIVALENT
RESISTANCE IN
PARALLEL
COMBINATION
Consider three resistances R1 , R2 & R3 connected in parallel combination with a power
supply of voltage
V.
Now
I = I1 + I2 + I3
according to Ohm’s law
V/R = I
Therefore,
V/Re = V/R1 + V/R2 + V/R3
V/Re = V(1/R1 + 1/R2 + 1/R3)
V/ReV = 1/R1 + 1/R2 + 1/R3
OR
JOULE'S LAW
INTRODUCTION:
When an electric current passes through a wire heat energy is produced. It is due to
the collision of
electrons with the atoms. In order to continue steady current, work has
to be done on electric charges.
STATEMENT:
Amount of work done on electric charge on steady current is directly proportional to
amount of heat.
Work Heat
PROOF:
Consider a conductor through which electric current q is passing in time t let the
potential difference
between two ends of wire is V.
We know that
v = W/q
or
W = q x V_(i)
According to Ohm’s law V = IR
putting the value of V in equation (i)
W = q x IR_______(ii)
But
I = q/t
Or
Q = It
putting the value of q in equation (ii)
W = It . IR
W = I2Rt
OHM'S LAW
INTRODUCTION
Ohm’s law is a quantitative relation b/w potential difference and electric current.
STATEMENT
According to Ohm’s law,
"The electric current passes through a conductor is directly proportional
to the potential differences between the ends of conductor,
if physical conditions of conductor remain constant."
i.e.
IV
I = kV
K =constant and is called "conductivity of material"
I/K = V
or
V = I/K
V = I x 1/K
Let [1/K = resistance]
V=IxR
GRAPHICAL REPRESENTATION