Properties of Electric Charge:

 Unlike charges(+q-q or -q + q)
Definition of Electric Charge attract each other while like
Types of Electric Charge
It is a basic characteristic of charges (+q+q or -q-q) repel each
Electric charges are classified into two other
matter to either attract or repel.
parts, positive charge which is carried by  Electric charges have additive
Electric charge is represented by
q. Unit of electric charge is protons (+1.6×10-19C) and negative property.
coulomb (C) electric charge which is carried by  Electric charges are quantised, i.e.,
electrons(-1.6×10-19C). q = ne, where n = number or
electrons, e = charge on electron.

Electric
Electric Charge, Potential
Charge Current and Difference
Voltage
Electric Current

Definition of Electric Current:

Electric current is defined as the
flow of electric charge per unit Electric Potential Energy: Potential of Difference
of time. When you charge an object, it The work required to move a
requires some effort to do so. single unit of charge from point
This effort is called work. The A to point B on a conductor
object then holds onto this work carrying an electric current is
Formula:
as electric potential energy known as the electric potential
When an electric charge (q) moves
difference between the two
through a conductor during a certain
points.
period of time (1), the resulting flow
of electric current (1) can be given as:
𝑞
𝑙 = 𝑡 𝑜𝑟 𝑞 = 𝑙𝑡 Electric Potential: Electric
Unit: Unit of electric current is potential is the amount of Formula:
Ampere(A) electric potential energy divided If you move a charge q from
by the charge. Thus, electric point A to point B on a
potential conductor and it takes work W,
Definition of 1A: 𝑒𝑙𝑒𝑐𝑡𝑟𝑖𝑐 𝑝𝑜𝑡𝑒𝑛𝑡𝑖𝑎𝑙 𝑒𝑛𝑒𝑟𝑔𝑦 then the potential difference (V)
=
1 𝑐𝑜𝑢𝑙𝑜𝑚𝑏 𝑐ℎ𝑎𝑟𝑔𝑒 between points A and B is given
1 𝑎𝑚𝑝𝑒𝑟𝑒 = 1 𝑠𝑒𝑐𝑜𝑛𝑑 ⇒ 1 𝐴 = 1 𝐶/𝑠 by:
When one coulomb of charge passes 𝑊
through a conductor in one second, the 𝑉 = 𝑉1 − 𝑉2
𝑄
current flowing through it, is referred to as Where, V1 = Potential at point
one ampere. Electric potential of two bodies A.
V2 = Potential at point B.
Unit: unit of electric potential
Direction of Electric Current: difference is: Volt(V)
Conventional current and
electron current flow in opposite
directions in metallic Definition of 1 Volt
conductors. 1 𝑗𝑜𝑢𝑙𝑒 𝐽
1 𝑣𝑜𝑙𝑡 𝑉 = 𝑜𝑟 𝐼𝑉 = 1𝐽𝐶 −1
1 𝑐𝑜𝑢𝑙𝑜𝑚𝑏 𝐶
If one joule of work is needed to move one
coulomb of charge from one point to another,
then the potential difference between those two
points is referred to as one volt.
Potential difference, which is measured in
Statement of Ohm's Law: Graphical Representation of Ohm's Law:
The voltage across the conductor is directly The plot of V versus I or I verous V forms a linear
proportional to the current flowing to the relationship that intersects the origin, O.
conductor, provided physical conditions and
temperature remain constant.
According to Ohm's law, V ∝ l
𝑉
i.e., V = (constant) 𝑙 ⇒ 𝑙 = 𝐶𝑜𝑛𝑠𝑡𝑎𝑛𝑡
The constant in the above relation is called
resistance (R) of the conductor.
𝑉
∴ 𝑙 = 𝑅 ⇒ 𝑉 = 𝐼𝑅
 Slope of V-I graph gives resistance

Electric Circuit
It is conducting which allows the current to
flow from one point to another.

Components of Electric Circuit Symols

An electric cell
Ohm’s
Resistance
Law
A battery or a combination of
cells
Plug key or switch (open)

Definition of Resistance: Plug key or switch (closed)

Resistance is how much a material resists the A wire Joint
flow of electricity. It's like a speed bump for
electrons. It's calculated by dividing the voltage Wires crossing without joining
by the current.
Unit:
Unit of resistance is Ohm represented as Ω.
Definition of 1 Ohm: Electric bulb
1 𝑣𝑜𝑙𝑡 1𝑉
1 𝑜ℎ𝑚 = ⇒ 1Ω =
1 𝑎𝑚𝑝𝑒𝑟𝑒 1𝐴
A resistor of resistance R
Variable resistance or rheostat
Factors Affecting the Resistance:
1. The resistance of a conductor is directly Ammeter
proportional to its length. i.e,
On increasing the length of a conductor, the Voltmeter
resistance of it also increases.
R∝l
Galvanometer
2. The resistance of a conductor is inversely
proportional to its cross-sectional area.
i.e., A decrease in the cross-sectional area of a
Resistivity or Specific Resistance:
conductor results in an increase in resistance.
The constant of proportionality 'p' is called specific resistance or
i.e,
1 resistivity of a material.
𝑅∝𝐴 p = RA/l
Combining above two equations: Unit of Resistivity:
ℓ ℓ The S,I unit of resistivity is ohm - m
𝑅 ∝ 𝐴 ⇒ 𝑅 = 𝑝𝐴 (p = constant of
proportionality).
 Combination
of Resistors

Resistors in Resistors in
series parallel

In series, the resistors are connected

end to end, creating a single path for
current flow. In parallel, the resistor are connected side by side,
creating multiple path for current flwo.

Equivalent Resistance of the Circuit:

Equivalent Resistance of the 1 1 1 1
𝑅
= 𝑅 + 𝑅 + 𝑅 {𝑅p < 𝑅1 , 𝑅2 , 𝑅3 }
Circuit: p 1 2 3

R5 = R1 + R2 + R3 (R5 > R1, R2, R3) Potential Difference:

Potential Difference: Vp=V₁=V2=V3
V5 = V 1 + V2 + V3 Total Current in the Circuit:
𝑉 𝑉 𝑉 𝑉p
Total Current in the Circuit: 𝐼Total = 𝐼1 + 𝐼2 + 𝐼3 = 𝑅1 + 𝑅2 + 𝑅3 = 𝑅
𝑉 +𝑉 +𝑉 𝑉 1 2 3 p
𝐿 𝑇𝑜𝑡𝑎𝑙 = 1 2 3 = 1
𝑅1 +𝑅2 +𝑅3 𝑅5

Properties of Resistors Connected in Parallel:

Properties of Resistors connected in  Potential difference is the same across all
Series: resistors in parallel i.e., V1 = V2 = V3
 Same current flows through each  The smallest resistance gets the most
resistor i.e, I1 = I2 = I3. current.
 Potential difference is different for each  The equivalent resistance R, is always less
resistors in series configuration. than any resistor in the parallel
 The resistors with the largest resistance configuration.
has the greatest voltage.  If 'n' identical resistances 'R' are connected
 The equivalent resistance R5 is always in Parallel, R then equivalent resistance,
greater than any resistor in the series R
configuration. 𝑅p = 𝑛
 If one point breaks in series circuit, the
total circuit will break.
 If 'n' identical resistances 'R' are
connected in series, then equivalent
resistance, R1 = nR.
 Electric Power & Heating
Effect of Electric Current

Heating effect happens due to resistance of a conductor

which impedes the flow of current and generates heat.

Electric Power Electric Energy

The rate at which electrical energy is

The amount of electrical work done or, the amount of
transferred or, the rate at which work is
electrical energy consumed over time.
done. i.e,
𝑊 Electrical Energy = Power consumed in watt Time
𝑃 = 𝑡 𝑜𝑟, 𝑃 = 𝑉𝐼 taken in hour
 Unit of power: watt (W) W = f 2Rt.
 Power P in terms of I and R: P = I2 × R Where, I = current in conductor, R = Resistance of
𝑉2 conductor t = Time for which current is passed
 Power P in terms of V and R : P =
𝑅 through conductor
 Relationship between watt and Joule: 1W =  Π It is measured in watt-hour or, kilowatt-
1Js-1 hour.
 Electric power is important because it  Π It is important because it determines the
determines the rate at which electric devices amount of electricity consumed by electrical
consume energy and amount of electricity devices and the cost of operating it over time.
required to operate them.  Relation between kilowatt-hour and joule:
 1 kWh = 3.6 x 106 J = 3.6 MJ
Definition of 1 watt
The power is said to be 1 watt, if 1 ampere of
current flows in a circuit against potential
difference of 1 volt.
1 watt = 1 volt × 1 ampere Joule's Law of Heating:
According to Joule's law of heating, amount of
heat produced in a conductor is directly
proportional to
 The square of the current flow through
the conductor (12).
 Resistance of the conductor (R)
 Time for which current is passed
through conductor (t)
Therefore, H ∝ I2 Rt ⇒ H = (constant) I2 Rt
= I2Rt