Ohm's law states that the voltage across a conductor is directly proportional to the current flowing through it, provided all physical conditions and temperatures remain constant. Resistance is a measure of opposition to current flow and depends on the material, length, and cross-sectional area of the conductor. The heating effect of electric current is used in various appliances like electric bulbs, heaters, and irons where a conductor is heated by the passage of current. Electric power is defined as the rate at which electrical energy is transferred by a circuit and is measured in watts.

1. ELECTRICITY
CLASS-X , SCIENCE
BY- HIMANSHU PATHAK
(TGT-SCIENCE)
RRSGS AMETHI

3. SYLLABUS
Effects of Current Electric current, potential difference and electric current.
Ohm’s law; Resistance, Resistivity, Factors on which the resistance of a
conductor depends. Series combination of resistors, parallel combination
of resistors and its applications in daily life. Heating effect of electric current
and its applications in daily life. Electric power, Interrelation between P, V, I
and R.

4. LIGHTNING IS ALSO ELECTRICITY

5. CHARGE

7. Unlike charges attract each other.

8. Like charges are repelling each other.

9. Those substances through which electricity can flow
are called conductors.
All the metals like silver, copper, aluminum etc. are conductors.
Those substances through which electricity cannot flow are
called insulators.
Glass, ebonite, rubber, most plastics, paper, dry wood, etc. are
insulators.

10. The electrostatic potential at any point is defined as the
work done in bringing a unit positive charge from infinity to that
point.
Potential is denoted by the symbol V and its unit is volt.
A potential of one volt at a point means that 1 joule of work is
done in bringing 1 unit positive charge from infinity to that point

14. The amount of work done in moving unit positive charge
from one point to another in an electric field is known as
potential difference.
Potential difference = Work done ∕Quantity of charge
transferred

15. If a W joule of work has to be done to transfer Q coulombs of
charge from one point to another point, then the potential
difference V between the two points is
given by the formula:
Potential difference, V = W/Q
The SI unit of potential difference is volt (V).

16. One volt is defined as the potential difference between
two points in a current carrying conductor when 1 joule of
work is done to move a charge of 1 coulomb from one
point to another .
Therefore,
1 volt = 1 joule / 1 coulomb

17. Voltmeter: The potential difference is measured by means of an
instrument called voltmeter.
The voltmeter is connected in parallel across the points where the
potential difference is measured.
A voltmeter has high resistance.

18. Electric Current: The electric current is the rate of flow of
electric charges (called electrons) in a conductor.
If a charge of Q coulombs flows through a conductor in time t
seconds, then the magnitude I of the electric current flowing
through it is given by
Current, I = Q/t

23. The SI unit of electric current is ampere and it is denoted by the
letter A.
AMPERE is a rate of flow of electric charges through a surface at
the rate of one coulomb per second.
Electric current is a scalar quantity.

24. An apparatus to measure electric current in a
circuit

25. A continuous conducting path in which a current can flow is
called an electric circuits.
It consist of electrical components like cell, lamps, meters ,
conducting wire etc.

30. Ohm’s law states that the voltage across a conductor is directly proportional to
the current flowing through it, provided all physical conditions and temperatures
remain constant.

34. Ohm’s law states that the voltage across a conductor is directly
proportional to the current flowing through it, provided all physical
conditions and temperatures remain constant.

36. V ∝ I
V = IR
“Ohms law states that the current flowing in a conductor
is directly proportional to the applied voltage across the
ends of the conductor at constant physical condition.”
Where, V = Potential difference across the ends of conductor,
I = current flowing through the conductor
R = proportionality constant also known as Resistance of the circuit.

37. • The SI unit of the resistance is Volt/Ampere which is also known as
“Ohm“.
• Resistance represents as by a symbol that is “Ω” (Omega)

39. Definition of 1 Ohm:-
“When the voltage at the ends of the conductor is 1 volt and
the current flowing in the conductor is 1 amp, the resistance
of the conductor will be 1 ohm.”

43. V-I graph characteristics
1.) This graph will be of a linear equation that will pass through the
origin.
2.) The V-I graph will be a straight line.
3.) As the value of voltage increases in the circuit, the value of the
current will also increase in the same proportion.
4.) The ratio of voltage and current will remain constant in all
phases.

44. Limitations of ohms law
1.) Ohms law is applicable to Ohmic conductors. For example – Copper, Aluminium , Silver
2.) Ohms law is not applicable for semiconductors (Diode & Transistor). Because after a certain
voltage there is a sudden rise in current which violates the linear equation of Ohm’s law.
3.) Ohms law is not valid when the physical conditions (temperature) vary. So, it is only
applicable at a constant temperature.
4.) According to the heating effect of electric current, a straight line gets a curve after a
certain high temperature. So, Ohm’s law fails for Ohmic conductors at high temperatures.

45. Application of Ohm’s law:-
1.) With the help of Ohms law, we can determine the value of Voltage, current
and resistance in an electrical circuit.
2.) Ohms law is used for electrical circuits. With the help of the Ohms law equation
V=IR, we can determine the equivalent resistance series and parallel circuits.
3.) Ohms law is also used to balance or maintain the desired potential or voltage
drop across the electronic elements.
4.) Ohms law is used for making Fuses of required resistance for the protection of
home appliances

47. “The measure of barrier or opposition to
current flow in any conductor or circuit is
resistance.”

48. Resistance is a measure of the opposition offered to the
current flow in an electric circuit.
Resistance is measured in ohms.

53. • Length of the conductor –
Resistance is directly proportional to the length of the conductor.

54. • Material of the conductor –
Resistance depends on the material of conductor. It is quantified by resistivity.
Resistance is directly proportional to resistivity.

55. • Area of the cross-section of the conductor –
Resistance is inversely proportional to the cross section area of the conductor.

56. Resistivity
The resistivity of a conductor is defined as the resistance offered by the
material per unit length for a unit cross-section.
Resistivity, commonly symbolized by the Greek letter
rho, ρ

60. Combination of resistance
• Two resistors are said to be
combined in series if they carry the
same current.
• Req = R1+R2
• Two resistors are said to be combined
in parallel if the same potential
difference is applied to them.
• 1/Req = 1/R1+ 1/R2

61. Equivalent Resistance of a System of Resistors
The equivalent resistance of two resistors is given as:
In series, Req = R1+R2
In parallel, 1/Req = 1/R1+ 1/R2

73. ADVANTAGES OF PARALLEL COMBINATION OVER SERIES COMBINATION ARE:
• In parallel combination each appliance gets the full voltage.
• If one appliance is switched on, others are not affected.
• The parallel circuit divides the current through the appliances. Each
appliance gets proper current depending on its resistance.

74. Power is commonly defined as the rate at which the work is done.
When this is done with respect to time and in an electrical circuit, it is
known as electric power.
Alternately, electric power is defined as the rate at which electric
energy is transferred across an electrical circuit per unit time.

75. Electrical Energy
The work done by a source of electricity to maintain a current in an electrical circuit is called
as electrical energy.
q= It
W= Vq
W= VIt
E= VIt

76. Electric Power
Electric power is defined as amount of electric energy
consumed in a circuit per unit time.
P = W/t
W=VIt
P = VIt/t
P=VI
V=IR
P=I2R
I= V/R
P= V2/R

77. S.I. unit of power is Watt.
Electric power is said to be 1 watt if 1 ampere current flows through
a circuit having 1volt potential difference
1 Horsepower =746 Watt
The department of electricity sells the electric energy to the
consumers in units called kilowatt-hour(kWh)

79. When an electric current is allowed to flow through a high resistance wire, such as
nichrome wire, the conductor heats up and produces heat. Such a heating action of a
conductor is known as the Heating effect of Current.
This is because of the fact that when an electric
current passes through it, fast electron collisions
start to occur. This concept or phenomenon is
known as the Heating Effect of Electric Current.

81. when an electrical current is passed through a conductor, it
generates excess heat due to the resistance caused by the
electrons in the conductor to the flowing current. The work done
in overcoming this resistance to the current generates what we
call heat in that conductor. The electrical heating effect of the
electrical current is most commonly and widely applied and used in
our daily life.

82. Let us assume a current I that is flowing through a resistor that has a resistance
of R as shown in the circuit. Let the potential difference across ends of the
terminals of the battery be V. Let us assume to be the time during which a
charge of Q amount flows across the circuit. The work which is done in moving
that charge Q through a potential difference V is V × I.

84. joule’s Law:
Heat (H) ∝ square of the current (I).
H ∝ Resistance of the given circuit.
H ∝ Time (t) for which current flows through the conductor.

85. Joule’s law of heating states that,
when a current ‘i ' passes through a conductor of resistance ‘r’ for time ‘t’ then the
heat developed in the conductor is equal to the product of the square of the current,
the resistance and time.
H=𝒊𝟐
×R×t

86. Let, an electric current, I is flowing through a resistor having resistance = R.
The potential difference through the resistor is = V.
The charge, Q flows through the circuit for the time, t
Thus, work done in moving of charge (Q) of potential difference (V),
W = V × Q
Since this charge, Q flows through the circuit for time t
Therefore, power input (P) to the circuit can be given by the following equation :
P = VI
P = V × Qt …..(i)

87. We know, electric current, I = Qt
Substituting Qt = I in equation (i), we get,
P = VI …(ii)
i.e., P = VI
Since, the electric energy is supplied for time ?, thus, after multiplying both sides of equation
(ii) by time t, we get,
P × t = VI × t = VIt ……(iii)
i.e., P = VIt
Thus, for steady current I, the heat produced (H) in time t is equal to VIt
H = VIt
i.e., H = VIt
We know, according to Ohm’s Law,
V = IR

88. by substituting this value of V in equation (iii), we get,
H = IR × It
H = I2Rt ……(iv)
The expression (iv) is known as Joule’s Law of Heating, which states that heat
produced in a resistor is directly proportional to the square of current given to the
resistor, directly proportional to the resistance for a given current and directly
proportional to the time for which the current is flowing through the resistor.

89. Electric Bulb: In an electric bulb, the filament of bulb gives light because of the heating effect of electricity. The
filament of bulb is generally, made of tungsten metal, having melting point equal to 3380°C.
Electric Iron: The element of electric iron is made of alloys having high melting poir^ Electric heater and geyser
work on the same mechanism.
Electric Fuse: Electric fuse is used to protect the electric appliances from high voltage if any. Electric fuse is
made of metal or alloy of metals, such as aluminum, copper, iron, lead, etc. In the case of flow of higher voltage
than specified, fuse wire melts and protect the electric appliances.
Fuse of 1A, 2A, 3A, 5A, 10A, etc., used for domestic purpose.
Suppose, if an electric heater consumes 1000W at 220 V.
Then electric current in circuit
I = PV
I = 1000W220V = 4.5 A
Thus, in this case of 5A should be used to protect the electric heater in the flow of higher voltage.

90. Consumption of electricity (electric energy) is generally measured in kilowatt.
Unit of electric energy is kilowatt-hour (kWh).
1 kWh = 1000 watt × 1 hour = 1 unit = 1000 W × 3600 s
1 kWh = 3.6 x 106 watt second = 3.6 × 106 J