This PPT is is related to physics. and this PPT is meant for educational purpose.

1. Electricity
Made by :-
B.SUBHASH
X - B

2. Types of charges
• There are two types of charges :-
• Positive charge :- These are made of sub
atomic particle proton.
• Negative charge :- These are made of
negative sub atomic particle electron.

3. S.I. unit of charge
• The S.I. unit of charge is coulomb.
• An electron posses a negative charge of
1.5 x 10-19.
• The S.I. unit of one coulomb is equivalent
to the charge containing 6.25 x 10-18.

4. Conductors and Insulators
Conductors
• These substance have
the property to conduct
electricity through them.
• These have free or
loosely held electrons
which helps in
conducting electricity.
• Example – copper.
Insulators
• These substance have
the property to obstruct
the flow of electricity.
• These do not have free
electrons present in them.
• Example – Rubber
Insulation.

5. Electric potential
• When a small electric charge is placed in
the electric field due to another charge, it
experiences a force. So, work has to be
done on the positive charge to move it
against this force of repulsion.
• The electric potential is defined as the
work done in moving a unit positive
charge fro infinity to that point.

6. Potential Difference
• The concept of electric potential is closely
linked to that of the electric field. A small
charge placed within an electric field
experiences a force, and to have brought that
charge to that point against the force
requires work. The electric potential at any
point is defined as the energy required to
bring a unit test charge from an infinite
distance slowly to that point.
• It is usually measured in volts, and one volt is
the potential for which one joule of work must

7. •

8. Voltmeter
• A voltmeter is an
instrument used for
measuring electrical
potential difference
between two points in
an electric circuit.
• Voltmeter has a high
resistance so that it
takes negligible
current.

9. Electric Current
•

10. Ammeter
• An ammeter is
a measuring
instrument used to
measure the electric
current in a circuit.
Electric currents are
measured
in amperes (A), hence
the name.
• An ammeter should
have a very low
resistance so that it may

11. Circuit Diagram
• We know that an electric circuit, as shown in
Fig. 12.1, comprises a cell(or a battery), a
plug key, electrical component(s), and
connecting wires. It is often convenient to
draw a schematic diagram, in which different
components of the circuit are represented by
the symbols conveniently used. Conventional
symbols used to represent some of the most
commonly used electrical components.

13. Georg Ohm
• Georg Simon Ohm (16
March 1789 – 6 July 1854)
was a German physicist and
mathematician. As a school
teacher, Ohm began his
research with the
new electrochemical cell,
invented by Italian
scientist Alessandro Volta.
Using equipment of his own
creation, Ohm found that
there is a direct proportionality
between the potential
difference (voltage) applied
across a conductor and the
resultant electric current. This

14. Ohm’s Law
• Ohm’s Law explains the relationship
between voltage (V or E), current (I) and
resistance (R)
• Used by electricians, automotive
technicians, stereo installers.
• According to Ohm’s law : At constant
temperature, the current flowing through a
conductor is directly proportional to the
potential difference across its end.

15. •

16. Resistance
• An electron traveling through the wires and
loads of the external circuit encounters
resistance. Resistance is the hindrance to the
flow of charge. For an electron, the journey
from terminal to terminal is not a direct route.
Rather, it is a zigzag path that results from
countless collisions with fixed atoms within the
conducting material. The electrons encounter
resistance - a hindrance to their movement.
• The S.I. unit of resistance is ohm’s (Ω).

17. Factors affecting Resistance
i. Length of conductor.
ii. Area of cross section of the conductor (or
thickness of the conductor).
iii. Nature of the material of the conductor,
and
iv. Temperature of conductor.

18. Resistivity
•

19. •

20. Resistivity of some common substances (200 C )

21. • The resistivity of alloys are much more
than those of pure metals (from which they
are made).
• For example the resistivity of magazines
(which is an alloy of copper, manganese
and nickel)is about 25 times more than
that of copper.
• Alloys are used in making heating a
materials as –
i. Alloys have very high resistivity (due to
which heating elements produce a lot of
heat on passing current).

22. Combination of Resistors
• Resistors can be combined in two
ways –
i. In series.
ii.In parallel.

23. Resistors in Series
• When two (or more) resistors are
connected end to end consecutively, they
are said to be connected in series.
• According to the law of combination of
resistance in series: The combined
resistance of any number of
resistances connected in series is
equal to the sum of the individual
resistances.
R= R1 +R2 +R3+………..

24. I. When a number of resistors connected in
series are joined to the terminal of a
battery, then each resistance has a
different potential difference across its
ends (which depends on the value of
resistance). But the total potential
difference across all the ends of all the
resistors in series is equal.
II. When a number of resistors are
connected in series, then the same
current flows through each resistance.

25. Resultant of Resistances connected in
Series
• The figure shows three resistances R1,R2,R3 connected
in series. Now suppose potential difference across
resistance R1 is V1 , R2 is V2 and R3 is V3. Let potential
difference across battery be V, then :
V = V1+V2+V3.
Applying Ohm’s law to the whole circuit : V = IR.
………..(1)
Applying Ohm’s law to the three resistors separately, we
get:
V1 = I x R1. ………………….. (2)
V2 = I x R2. ………………….. (3)
V3 = I x R3. ………………….. (4)
Substituting (2), (3), (4) in (1)
IR = IR1 + IR2+ IR3
OR, IR= I (R1+R2+R3)
Or, R = R1+R2+R3 .

26. Resistors in Parallel
• When two (or more) resistors are connected
between the same points, they are said to be
connected in parallel.
• According to the law of combination of
resistance in parallel: The reciprocal of the
combined resistance of any number of
resistances connected in parallel is equal
to the sum of the reciprocals of the
individual resistances.
1/R= 1/R1 +1/R2 +1/R3+………..
• When a number of resistances are connected
in parallel then their combined resistance is

27. • When a number of resistance are connected in
parallel, then the potential difference across
each resistance is same which is equal to the
voltage of battery applied.
• When a number of resistances connected in
parallel are joined to the two terminals of a
battery, then different amounts of current flow
through each resistance (which depend on the
value of resistance). But the current flowing
through each parallel resistance, taken together,
is equal to the current flowing in the circuit as a
whole. Thus, when a number of resistance are
connected in parallel, then the sum of current
flowing through all the resistances is equal to the

28. Resultant of Resistances connected in
Parallel
• The figure shows three resistances R1,R2,R3 connected
in series. Now suppose currant across resistance R1 is I1
, R2 is I2 and R3 is I3. Let total current in the circuit be I,
then:
I = I1+I2+I3.
Applying Ohm’s law to the whole circuit : I = V/R.
………..(1)
Applying Ohm’s law to the three resistors separately, we
get:
I1 = V / R1. ………………….. (2)
I2 = V / R2. ………………….. (3)
I3 = V / R3. ………………….. (4)
Substituting (2), (3), (4) in (1)
V/R = V/R1 + V/R2+ V/R3
OR, V/R= I (1/R1 +1/R2 + 1/R3)
Or, 1/R = 1/R1+1/R2+1/R3 .

29. Parallel and Series connection
Parallel connection
• If one electric appliance stops
working due to some defect,
then all other appliances keep
working normally.
• In parallel circuits, each
electric appliance has its own
switch due to which it can be
turned on or off independently.
• Each appliance gets same
voltage as that of power
source.
• Overall resistance of
household circuit is reduced
Series connection
• If one electric appliance stop
working due to some defect,
then all other appliances stop
working.
• All the electric appliances
have only one switch due to
which they cannot be turned
on or off separately.
• In series circuit, the
appliances do not get same
voltage (220 V) as that of the
power supply line.
• In series circuit the overall
resistance of the circuit

30. Heating effect of electric current
• When electricity passes through a high
resistance wire like a nichrome wire, the
resistance wire becomes very hot and
produces heat. This is called the heating
effect of current.

31. James Prescott Joule
James Prescott Joule (24 December
1818 – 11 October 1889) was an
English physicist and brewer, born
in Salford, Lancashire. Joule studied the
nature of heat, and discovered its
relationship to mechanical work. This led to
the law of conservation of energy, and this
led to the development of the first law of
thermodynamics. The SI derived unit of
energy, the joule, is named for James
Joule. He worked with Lord Kelvin to
develop the absolute scale of temperature.
Joule also made observations of
magnetostriction, and he found the
relationship between the current through
a resistor and the heat dissipated, which is
now called Joule's first law.

32. Joule’s law of heating
Let
An electric current I is flowing through a resistor having resistance
equal to R.
The potential difference through the resistor is equal to V.
The charge Q flows through the circuit for the time t.
Thus, work done in moving of charge Q of potential difference V = VQ
Since, this charge Q flows through the circuit for time t,

33. • The heat produced in wire is directly
proportional to
i. Square of current.
ii. Resistance of wire.
iii. Time for which current is passed.

34. Applications of heating effect of electric
current
There are many practical uses of heating effect of current. Some of the
most common are as follows.
• An incandescent light bulb glows when the filament is heated by heating
effect of current, so hot that it glows white with thermal radiation (also
called blackbody radiation).
• Electric stoves and other electric heaters usually work by heating effect
of current.
• Soldering irons and cartridge heaters are very often heated by heating
effect of current.
• Electric fuses rely on the fact that if enough current flows, enough heat
will be generated to melt the fuse wire.
• Electronic cigarettes usually work by heating effect of current, vaporizing
propylene glycol and vegetable glycerin.
• Thermistors and resistance thermometers are resistors whose
resistance changes when the temperature changes. These are
sometimes used in conjunction with heating effect of current(also called
self-heating in this context): If a large current is running through the
nonlinear resistor, the resistor's temperature rises and therefore its
resistance changes. Therefore, these components can be used in a
circuit-protection role similar to fuses, or for feedback in circuits, or for

35. Electric Energy
• H = I2 Rt gives the rate at which electric energy is dissipated or
consumed in an electric circuit. This is also termed as electric
power. The power P is given by
P = VI
Or P = I2R = V2/R
• The SI unit of electric power is watt (W). It is the power consumed
by a device that carries 1 A of current when operated at a potential
difference of 1 V. Thus,
1 W = 1 volt × 1 ampere = 1 V A
• The unit ‘watt’ is very small. Therefore, in actual practice we use a
much larger unit called ‘kilowatt’. It is equal to 1000 watts. Since
electrical energy is the product of power and time, the unit of electric
energy is, therefore, watt hour (W h). One watt hour is the energy
consumed when 1 watt of power is used for 1 hour. The commercial
unit of electric energy is kilowatt hour (kW h), commonly known as
‘unit’.
1 kW h = 1000 watt × 3600 second
= 3.6 × 106 watt second
= 3.6 × 106 joule (J)