Glance to electricity - Class- X- physics

1. Class-X - Physics
Electricity

2. Understanding the Lesson:
• Current electricity Electric charge
• Electric current Direction of current
• Electric potential difference Electric circuit
• Circuit diagram Measuring instruments
• Ohm’s law V-I graph
• Resistance
• Symbols of commonly used component in circuit
• Heating effect of electric current & its practical applications

3. Let's take a closer look at Electricity and
find out how it works!
• Electricity is the most versatile (means it is flexible
and resourceful) energy source that we have;
Electricity has played a vital part of our past. But it
could play a different role in our future, with many
more buildings generating their own renewable electric
power using solar cells and wind turbines.

4. What is Electricity?
• Basic concept: If you've ever sat watching a thunderstorm, with mighty
lightning bolts darting down from the sky, you'll have some idea of the power
of Electricity. A bolt of lightning is a sudden, massive surge of electricity
between the sky and the ground beneath. The energy in a single lightning bolt is
enough to light 100 powerful lamps for a whole day or to make a couple of
hundred thousand slices of toast!
• Electricity is a type of energy that can build up in one place or flow from one
place to another. When electricity gathers in one place it is known as static
electricity (the word static means something that does not move); electricity
that moves from one place to another is called current electricity.

5. Questions Arises In Mind
• What constitutes electricity ?
• How does it flow in an electric circuit ?
• What are the factors that control or regulate the current through an electric circuit ?
• How does current and electron flow in a circuit?
• What does a switch do?
• How do we express electric current?
• How does the metal conduct electricity?
• How does an electric bulb lights up as soon as we turn the switch on?
• What makes the electric charge to flow?
• Is there a relationship between the potential difference across a conductor and the
current through it?
• The current is different for different components ,why do they differ?
• To maintain the current the source has to keep expanding its energy, where does this
energy go?
• What happens to the energy expanded by the source?

6. Verify Your Answers
• What constitutes electricity ?
• Electricity is a form of energy. Electricity is the flow
of electrons. The flow of electric charges across a
cross-section of a conductor constitutes an electric
current. For example, a stream of electrons moving
through a conducting wire constitutes an electric
current.
• How does it flow in an electric circuit ?
Current only flows when a circuit is
complete—when there are no gaps in it. In a
complete circuit, the electrons flow from
the negative terminal (connection) on the
power source, through the connecting
wires and components, such as bulbs, and
back to the positive terminal.

7. • What are the factors that control or
regulate the current through an electric
circuit ?
The factors to control or regulate the
current through an electric circuit are:
Resistance.
Voltage.
• How does current and electron flow in a circuit?
The flow of electrons is termed electron current.
Electrons flow from the negative terminal to the
positive. Conventional current or simply current, behaves
as if positive charge carriers cause current flow.
Conventional current flows from the positive terminal to
the negative.
• What does a switch do?
A switch makes a conducting
link between the cell and the bulb.
• How do we express electric
current?
Electric current is denoted by
letter 'I'. Electric current is
expressed by the rate of flow
of electric charges. Rate of flow
means the amount of charge
flowing through a particular area in
unit time. Where, I is electric
current, Q is net charge and t is
time in second.

8. • How does the metal conduct electricity?
Metals conduct electricity because the electrons inside
the metal are relatively free to move. So
when electricity is pass through metals, electrons
carry electricity and spread it all over the metal. All
metals conduct electricity to a certain extent, but
certain metals are more highly conductive.
The most highly conductive metals are silver, copper,
and gold. Copper, Pure silver is the most conductive
of all metals.
• How does an electric bulb lights up as soon as we
turn the switch on?
When we close the circuit, the electric field is
established instantly with the speed of electromagnetic
wave which cause electron drift at every portion of the
circuit. Due to which the current is set up in the entire
circuit instantly. It is due to this reason, the electric
bulb glows immediately when switch is on.
• What makes the electric charge to flow?
Electric current or electric charges
flow because of the Coulomb's force on
them . The force is due to electric field.
The field is created because of potential
difference between two end points of a
conductor. When a voltage is applied
across a conductor, a circuit is complete,
the conductor has one side +ve and other -
ve, electrons from -ve side are repelled and
+ve side attracts electrons, so electrons are
made to flow causing current to flow in
reverse direction.

9. • Is there a relationship between the potential
difference across a conductor and the current
through it?
Ohm's law is the relationship between potential
difference across a conductor and the
current flowing through it. Ohm's law states that
"The current flowing through a conductor is
directly proportional to the potential difference
between its ends provided its temperature remains
constant.
• The current is different for different components,
why do they differ?
current is caused by the movement of electrons in a
certain direction, this movement of electrons is
different in different substances, some compounds
produce higher resilience to the electrons resulting
into a higher resistance and higher resistance means
lower current. at the same time some compounds
allow free motion of electrons so lower resistance
thus higher current.
• To maintain the current the source has to keep
expanding its energy, where does this energy go?
We know that a battery or a cell is a source of electrical
energy. The chemical reaction within the cell generates
the potential difference between its two terminals that
sets the electrons in motion to flow the current through
a resistor. A part of this source energy in maintaining
the current may be consumed into useful work (like in
rotating the blades of an electric fan). Rest of the
source energy may be expended in heat to raise the
temperature (heating effect). Example: an electric fan
becomes warm if used continuously for longer time
etc. On the other hand, if the electric circuit is purely
resistive, that is, a configuration of resistors only
connected to a battery, the source energy continually
gets dissipated entirely in the form of heat.

10. Know the Fundamentals of Charge
 An atom is a fundamental unit of matter made up of
• protons (with a positive charge)
• neutrons (neutral – no charge)
• electrons (with a negative charge)
 Everything is made of atoms which contain POSITIVE particles called
PROTONS and NEGATIVE particles called ELECTRONS.
 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.
 Electric charge is given the symbol Q
Electrons are the charge carriers that flow in an electrical circuit –from
the negative to positive terminals.

11. Electric circuits
• An electric current is a flow of electric charges.
• For an electric current to happen, there must be a circuit. A circuit is a closed path or
loop around which an electric current flows. A circuit is usually made by linking
electrical components together with pieces of wire cable. Thus, in a flashlight, there is a
simple circuit with a switch, a lamp, and a battery linked together by a few short pieces
of copper wire. When you turn the switch on, electricity flows around the circuit. If
there is a break anywhere in the circuit, electricity cannot flow. If one of the wires is
broken, for example, the lamp will not light. Similarly, if the switch is turned off, no
electricity can flow. This is why a switch is sometimes called a circuit breaker.

12. Electric Current and Circuit (Key points)
• If the electric charge flows through a
conductor through a metallic ware there is an
electric current in the conductor.
• The cell or battery when placed in proper
order provide flow of charges or an electric
current through the torch bulb to glow, the
torch gives light only when its switch is on.
• Switch makes a conducting link between the
cell and the bulb.
• A continuous and closed path of an electric
current is called an electric circuit if the
circuit is broken anywhere or the switch is
turned off of the current stops flowing and
the bulb does not glow.
• Electric current is expressed by the
amount of charge flowing through a
particular area in unit time it is the
rate of flow of electric charges.
• In circuits using metallic wears
electrons constitute the flow of
charges electric current. It is
considered to be the flow of positive
charges.
• In an electric circuit the direction of
electric current is taken as opposite to
the direction of the flow of electrons
which are negative charges.

13. •An instrument called ammeter measures electric
current in a circuit it is always connected in series
in a circuit through which the current is to be
measured.
•The electric current flows in the circuit from the
positive terminal to the cell to the negative
terminal of the cell through the bulb and ammeter.
•A current starts only when an electron from one
terminal to the electric supply physically reaches
the other terminal through the bulb because the
physical drift of electrons in the conducting where
is a very slow process.
•If a net charge Q flows across any cross
section of a conductor in time t then the
current I, through the cross section is
I=Q/t => t = Q / I
•The SI unit of electric charge is coulomb
(C).
•Coulomb is equivalent to the charge
contained in nearly 6×108 electrons.
•The electric current is expressed by a unit
called ampere A.
•1 ampere is constituted by the flow of one
coulomb of charge per second. A=1C/1s.
Small quantities of current are expressed
in milliampere (1mA = 10-3A) or in
microampere (1µA = 10-6A)
Key points. Contd……

14. Electric Potential And Potential Difference
• The electrons move only , if there is a
difference of electric pressure- called the
potential difference- along the conductor.
• When the cell is connected to a conducting
circuit element, the potential difference sets the
charges in motion in the conductor and
produces an electric current.
• The electric potential difference between two
points in an electric circuit carrying some
current as the work done to move a unit charge
from one point to the other-
Potential difference(V) between two points =
work done W / Charge Q ,
V = W / Q
•The SI unit of electric potential
difference is volt(V).
• One volt is the potential difference
between two points in a current carrying
conductor, when 1joule of work is done
to move a charge of 1coulomb from one
point to the other.
• 1 volt = 1joule / 1 coulomb
• 1V = 1 JC-1

15. What is an insulator?

16. Conductors & Insulators
• What makes something a good conductor?
Conductors conduct electrical current very easily because of their free
electrons. Insulators oppose electrical current and make poor conductors.
Some common conductors are copper, aluminum, gold, and silver. Some
common insulators are glass, air, plastic, rubber, and wood.
• Good conductors allow electrons to move through them easily. Insulators do
not
allow electrons to move easily.

17. Conductors Insulators
•Conductors are materials that allow free
flow of electrons from one atom to another.
•Conductors conduct electricity because of
the free electrons present in them.
•These materials can pass electricity through
them.
•Atoms are not able to hold onto their
electrons tightly.
•Materials that are good conductors
generally have high conductivity.
•Mostly metals are good conductors such as
copper, aluminum, silver, iron, etc.
Distinguish Between Conductor And Insulators
•Insulators won’t allow free of electrons from
one atom to another.
•Insulators insulate electricity because of the
tightly bound electrons present within atoms.
•Insulating materials cannot pass electric
current through them.
•Atoms have tightly bound electrons thereby
unable to transfer electrical energy well.
•Good insulating materials usually have low
conductivity.
•Common insulators include rubber, glass,
ceramic, plastic, asphalt, pure water, etc.

18. Circuit Diagram
•A circuit is a simplified systematic
representation of the components of an
electrical circuit.
•An electrical circuit, comprises a cell , a plug
key, electrical components and connecting
wires.
•Conventional symbols used to represent the
most commonly used electrical components.

19. Measuring Instruments
• Ammeters : it is used to measure the magnitude of
electric current through any wire of a circuit.
 It is always connected in series.
 It should have low resistance.
• Voltmeter: It measures the potential difference
between two points of the circuit.
The voltmeter is always connected in parallel
across the points between which the potential
difference is to be measured.
It should have high resistance.

20. Ohm’s Law
• Ohm’s Law explains the relationship between the current I, flowing in a metallic wire and
the potential difference across its terminals. i.e. voltage (V or E), current (I) and resistance
(R)
• Used by electricians, automotive technicians, stereo installers.
• According to Ohm’s law : The potential difference V, 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.
• Vα I => V / I = constant = R => V = IR , where R is a constant , is called
Resistance.
• Resistance is the property of a conductor to resist the flow of charges through it. It is
measured in Ohm (Ω).

21. •1ohm = 1volt / 1 ampere
• If the potential difference across the two ends of a conductor is 1V and the current through it is 1A,
then the resistance R, of the conductor is 1 Ω.
•I = V/ R, The current through a resistor is inversely proportional to its
resistance. If the resistance is doubled the current gets halved.
• 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.
• A component used to regulate current without changing the voltage source is called variable
resistance.
•A rheostat is a variable resistor which is used to control current. They are able to vary the resistance
in a circuit without interruption. ... Therefore they are mostly constructed as wire wound resistors.
Resistive wire is wound around an insulating ceramic core and the wiper slides over the windings.
Ohm (Ω) and Rheostat

22. V-I graph
• 1. circuit diagram:
• 2. variation of current with potential difference
• Slope of V-I curve gives resistance
R=Slope= ∆V/∆I
• I-V curve of Ohm’s law

23. • Resistance of a uniform metallic conductor is directly proportional to its length(l)
R α l
• Resistance is inversely proportional to area of cross- section A
R α 1/A
R α l/A
 R = ρ l/A
Where rho (ρ) is constant of proportionality and it is called electric resistivity of the
material of the conductor.
• Resistance of a metallic conductor also depends on temperature.
• It also depends on the nature of the material.
Factors effecting resistance of a Conductor

24. Electric Resistivity (ρ)
 Resistivity depends on the nature of the material and temperature. It is
independent of the length and area of cross- section of the conductor. SI unit of
resistivity is Ωm.
 ρ = RA/ l
 Where, R resistance
 A = area of cross – section
 l = length of conductor
Classification of elements on the basis of resistivity:
 Metals and alloys have very low is it in the range of 10 - 8 Ωm to 10 - 6 Ωm . they
are good conductors of electricity.
Insulators have resistivity of the order of 1012 to 1017 Ωm. they are bad conductors
of electricity

25. Use of elements on the basis of Resistivity:
Copper and Aluminium are used for electric transmission lines because both
posses low resistivity,
 alloys are commonly used in electric heating appliances
Resistivity of an alloy is generally higher than that of its constituent metals do
not oxidize readily at high temperature for this reason they are commonly used
in electric heating device.
Electric Resistivity (ρ) contd…….

26. Resistivity of some common substances (200 C )

27. Resistivity of some common substances (200 C )…. Contd….
• The resistivity of alloys are much more than those of
pure metals (from which they are made).
• For example the resistivity of maganine (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).
ii. Alloys do not undergo oxidation easily even at
high temperature

28. Combination of Resistances
Resistances in series
• Circuit diagram
• The current is same through each resister
• The total voltage drop across the
combination is always equal to the sum
of voltage or potential drop across
individual resistors . V = V1 + V2 + V3
• The equivalent resistance is equal to
sum of individual. R eq = R1 + R2 + R3
Resistances in parallel
• Circuit diagram
• The total current in the circuit is sum of
separate currents through each branch. I =
I1+I2+I3
• Difference across each resistor is same and
equal to potential difference applied.
• Reciprocal of equivalent resistance is
equal to the sum of reciprocal of individual
resistance. 1 /R eq = 1/R1 +1/ R2 + 1/R3

29. Special case
Resistance in series
• When n number of
identical resistors having
resistance ‘R’ is
connected in series then
equivalent resistance
becomes
• Req = nR
Resistance in parallel
• When n number of
identical resistors having
resistance ‘R’ is
connected in parallel then
equivalent resistance
becomes
• Req = R/n

30. • Series
• The same amount of current flows through
all the components.
• In an electrical circuit, components are
arranged in a line
• When resistors are put in a circuit, the
voltage across each resistor is different
even though the current flow is the same
through all of them.
• If one component breaks down, the whole
circuit will burn out.
• If Vt it total voltage then it is equal to
V1+V2+V3
Difference Between Series and Parallel Circuits
• Parallel
• The current flowing through each components
combines to form the current flow through the
source.
• In an electrical circuit, components are
arranged parallel with each other.
• When resistors are put in this circuit, the
voltage across each of the resistors is the same.
And even the polarities are the same.
• Other components will function even if one
component breaks down, each has its own
independent circuit
• If Vt it total voltage then it is equal to
V1=V2=V3

31. Key Differences Between Series and Parallel Circuit
• The components in a series circuit are arranged in a single path from one end of
supply to another end. However, the multiple components in a parallel circuit are
arranged in multiple paths wrt the two end terminals of the battery.
• In a series circuit, a common current flows through all the components of the
circuit. While in a parallel circuit, a different amount of current flows through
each parallel branch of the circuit.
• In the series circuit, different voltage exists across each component in the circuit.
Whereas in the parallel circuit, the same voltage exists across the multiple
components in the circuit.
• A fault in one of the components of the series circuit causes hindrance in the
operation of a complete circuit. As against fault in a single component in a
parallel network do not hinder the functioning of another part of the circuit.
• The detection of a fault in case of a series circuit is difficult, but it is quite easy
in parallel circuits.
• The equivalent resistance in case of a series circuit is always more than the
highest value of resistance in the series connection. While the equivalent
resistance in the parallel circuit is always less than any of the individual
resistances in parallel combination.

32. Some important points for series and parallel combination
• For getting maximum equivalent resistance, all
registered should be connected in series and for getting
minimum equivalent resistance, all registered should be
connected in parallel
• In domestic circuits, parallel combination is used
because in series arrangement, if anyone of appliances
fails or is switched off, all the other appliances stop
working.

33. Electric Power
• Electric power(P): the rate at
which electric energy is consumed
or dissipated is called electric
power. Electric power:
 P= VI = I2R = V2 / R
• SI unit of electric power is watt(W)
• One Watt (1W):One watt is the
power consumed by a device that
carries 1A of current when
operated at a potential difference
of 1V.
Thus, 1W = 1 volt X 1 ampere = 1VA
• Larger unit of Power
1kW = 1000W (1kW = one kilowatt)
Commercial unit of electric energy (kWh)
• 1kWh = 1000watt X 3600seconds
• 1unit = 1kWh = 3.6 X 106J
• One kilowatt hour is the energy
consumed when 1kilowatt of power is
used for one hour.

34. • Heating effect: When an electric
current passes through a high
resistance wire like nichrome wire,
the wire gets heated and its
temperature rises, i.e. the resistance
wire becomes very hot and produces
heat. This is known as heating effect
of Electric Current.
• Joule’s law of heating: Heat produced
in a conductor is directly proportional
to:
 Square of current for a given resistor
( H α I2)
 The resistance for a given current
(H α R)
 The time for which the current flows
through the resistor (H α t)
 H = I2Rt
Heating effect of electric current

35. 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 many other
purposes. In general, self-heating can turn a resistor into a nonlinear and hysteretic circuit element.

36. Practical applications of heating effect of electric current
• Incandescent electric lamp: the heating effect of electric
current is also used to produce light like in a electric
bulb the filament of the bulb is made up of tungsten
with high melting point 3380 degree centigrade it is
thermally isolated using insulated support presence of
chemically inactive gases like argon and nitrogen
prolong the life of the filament when voltage is applied
across the filament of the bulb the current starts passing
through it the filament gets heated to a very high
temperature 2700 degree centigrade it becomes white
hot and start radiating heat and light

37. • Fuse : fuse is a device which is based on the
principle of heating effect of electric current it
protect circuits and appliances why stopping
the flow of any unduly high current it consist a
piece of wire made of a metal or an alloy of
appropriate melting point in a current larger
than the specified value flows through the
circuit the temperature of the fuse wire
increases this melts the fuse wire and breaks
the circuit.
Practical applications of heating effect of electric current

38. 2020