**Electricity is a major part of our lives**

**Electric charge: **Electric charge is a property of matter by which
it can attract or repel other charged matter. For eg. proton, electron, ions,
etc.

- The SI unit of charge is Coulomb, represented by a
letter Q.
- One electron posses a charge of 1.6*10^-19C.
- One Coulomb of charge is contained in 6.25*10^18
electrons.

**Types of electric
charges:**

- Positive charge
- Negative charge

**Properties of electric
charges:**

- Like charges repel each other
- Unlike charges attract each other.

**Conductors and Insulators**

**Conductors: **

- Substances which allow the electric charges to flow
through them are called conductors.
- Conductors have this property due to the presence of
free charges(electrons) in them.
- For eg. Iron, Silver, gold, etc.

**Insulators:**

- Substances which do not allow electric charges to flow
through them are called insulators.
- Insulators do not have this property because they lack
free charges(electrons) in them.
- For eg. Rubber, Wood, Plastic, etc.

**Electric Potential**

1.
The electric potential
at any point in an electric field is defined as the amount of work done in
bringing a unit test positive charge from infinity to that point.

2.
SI unit of electric
potential is Volt.

3.
Electric potential is
also known as Voltage.

4.
It is denoted by the
symbol V.

**Potential Difference**

1.
The amount of work done
in bringing a unit test positive charge from one point to another point in an
electric field is called the potential difference.

2.
SI unit of potential
difference is volt.

3.
It is also called
Voltage.

4.
It is denoted by the
symbol V

Potential difference is
also defined as Work done/Quantity of charge moved

Thus,

*Potential Difference = Work Done/Quantity of
charge moved*

*Or, V = W/Q*

- If one joule of work is done in moving a charge of 1
coulomb across two given points then there is a potential difference of 1
volt across these two points.
- Potential difference is measured by a device called a
voltmeter.
- A voltmeter has high resistance.
- A voltmeter is always connected in parallel across the
points where the potential difference is to be measured.

**ELECTRIC CURRENT**

**Electric current: **

**Electric current is the rate of flow of electric charges in a conductor.**- SI unit of Electric current is Ampere.
- Electric current is denoted by a letter I.
- Electric current is also defined as the Quantity of
charge moved/ Time taken.

*Electric Current = Quantity of charge moved/
Time taken*

*Or, I = Q/t*

~When 1 coulomb of
charge is moved every second in a given cross-section of a conductor then 1
ampere of electric current is said to flow in that conductor.

~Electric current is
measured by a device called an ammeter.

~An ammeter should have
a very low resistance so that it can give an accurate reading.

~A continuous flow of
electric current in a circuit is maintained by maintaining a potential
difference in it. Potential difference is maintained by using a power source
such as a battery.

~The direction of
conventional current is from the positive terminal of the battery to the
negative terminal of the battery.

**Electric circuit: **A continuous conducting path which consists of
connecting wires, switches, resistors, etc connected to the two terminals of a
battery through which the current flows is called an electric circuit.

**Types of electric
circuit**

- Open circuit
- Closed circuit

**Open circuit: **

·
Switch is open in open
circuit

·
Electric current does not
flow in open circuits

**Closed circuit:**

·
Switch is closed in
closed circuit.

·
Electric current flows
in closed circuit

# Circuit Diagrams

· Diagrams which are used to represent the components of an electric circuit using electrical symbols are called circuit diagrams.

### OHM'S LAW

·
**Ohm's
law states that the potential difference across the ends of a conductor is
directly proportional to the electric current flowing through it, provided the
temperature the temperature is constant.**

The formula through which ohm's law is generally
represented is given below-

# V = IR

In the above given formula,

V
= Voltage

I
= Current

R
= Resistance

Above given formula can also be written as,

**I
= V/R**

**or,
R = V/I**

·
The ratio of potential difference and
electric current is always a constant called resistance.

**Resistance: **Resistance is a
property of material which obstruct the flow of electric charges in a material.
**The resistance of a conductor depends
upon its length, thickness, material and temperature.**

·
The
substance which has more resistance provides more obstruction to the electric
current flowing through it.

·
Thus,
resistance is inversely proportional to electric current.

**From ohm's law
we get these two relations:**

** i.
****Potential
difference is directly proportion to electric current.**

** ii.
****Electric current
is inversely proportional to resistance.**

Thus,
electric current flowing in a conductor depends upon these two factors:

i.
Potential
difference across the ends of a conductor.

ii.
Resistance
of the conductor.

# Graph of Ohm's law

·
The graph of ohm's law is a straight
line.

·
Graph of ohm's law is a straight line
because the ratio of potential difference and electric current remains the same
in constant temperature.

# Good conductors, resistors and insulators

·
**Good
conductors: **Substances which provide a very less
resistance to electric current are called good conductors. for eg. silver,
iron, copper etc.

·
**Resistors:
**Substances
which provide relatively more resistance than good conductors are called
resisitors. for eg. Nichrome, Manganin, etc.

·
**Insulators:
**Substances
which provide an infinite amount of resistance to the electric current are
called insulators. for eg. rubber, wood, plastic, etc.

# Factors affecting the resistance of a
conductor

**Given
below are the factors which affect the resistance of a conductor**

i.
Length of the conductor.

** ii.
****Area
of cross-section of conductor.**

** iii.
****Nature
of the material.**

** iv.
****Temperature
of the conductor.**

**Effect of length
of conductor**

·
**The length of a
conductor is directly proportional to the resistance of conductor.**

**Effect of area
of cross-section of conductor**

·
**The area of
cross-section is inversely proportional to the resistance of conductor.**

**Effect of nature
of material**

·
**Every material
has its inbuilt resistance which also triggers resistance further. This inbuilt
resistance is also called resistivity represented by a symbol called
rho.**

**Temperature of
the conductor**

·
**Resistance of a
conductor is directly proportional to the temperature of the conductor.**

·
**However
temperature does not affect the resistance of resistors like alloys.**

*From above given
factors we get a formula for resistance of any material which is related to its
physical features.*

**R = pL/A**

__Where, R =
Resistance__

__p = resistivity
of the material__

__L = Length of
the material__

__A = Area of
cross-section of material(Thickness)__

**Area of
cross-section: **Area
of cross-section just refers to the thickness of the material.

# COMBINATION OF RESISTORS

Resistors can be connected in two combinations given
below

i.
Series connection

ii.
Parallel connection

**Series
connection: **

·
When resistors are connected end to end
with each other, they are said to be connected in series connection.

·
Potential difference across the ends of
each resistor is not same in this connection.

·
Electric current is same in all the
resistors connected in series.

**Parallel
connection: **

·
When resistors are connected between the
same two points, they are said to be connected in parallel.

·
Potential difference across the ends of
each resistor is same in this connection.

·
Magnitude of electric current flowing in
each resistor in this connection is not same.

**Equivalent
resistance: **

·
Equivalent resistance is the resultant
resistance of all the resistors connected in a particular combination.

·
Equivalent resistance of a series
connection of resistors is always more than the resistance of all the
resistors.

·
Equivalent resistance of a parallel
connection is always less than the resistance of an individual resistor having
the least resistance in the connection.

**Given
below is the formula for equivalent resistance in series connection**

**R _{s
} = R**

_{1 }**+ R**

_{2 }**+ R**

_{3}**.....**

**Given
below is the formula for equivalent resistance in parallel connection**

**1/R**_{S }**=
1/R**_{1
}** + 1/R**_{2
}** + 1/R**_{3}**.....**

**Advantages
of parallel connection over the series connection in the domestic circuit.**

i.
In parallel connection, if due to any
effect an appliance stops working, all the appliances in the house keep on
working and no effect is created.

ii.
In parallel connection, there is a
separate switch for each appliance in the house.

iii.
Every appliance gets the same voltage as
from the power source.

iv.
In parallel connection, overall
resistance is not so much which provides adequate amount of electric current to
each appliance.

**ELECTRIC
POWER**

**Electric
Power: **The amount of electrical work done per unit time is
called electric power.

**P
= VI**

Where,
P = Power

V
= Potential Difference

I
= Electric current

The formula of electric power is given above.

# Unit of Electric power

The SI unit of electric power is Watt. The power of
1 watt is the rate of working at 1 joule per second.

**Some
other formula to calculate electric power**

**P
= I ^{2}R**

**P
= V ^{2}/R**

**Formula
to calculate electric energy**

**E
= Pt**

Where,
E = Electrical energy

P
= Power

t
= Time

# COMMERCIAL UNIT OF ELECTRICAL ENERGY

·
**The
commercial unit of electrical energy is Kilo-Watt hour or kWh.**

·
One Kilo-Watt hour is that amount of
energy which is consumed by an electric appliance having a power rating of 1
kilo-watt in 1 hour.

·
1 Kilo-watt hour is equal to 36,00,000J
of electrical energy.

# HEATING EFFECT OF ELECTRIC CURRENT

When an electric current is passed through a
conductor it heats up, this is called heating effect of electric current.

**Formula
to calculate heat generated by electric current**

**H
= I ^{2}Rt**

Where H = Heat energy

I = Electric current

R = Resistance

t = Time

Ã˜ __Heating effect of electric current is also called joule's law of heating.__

**Other
formula to calculate heat generated by electric current.**

**H
= VIt**

**H
=V ^{2}t/R**

**Some
applications of heating effect of electric current**

i.
Heating effect of electric current is
used in many electrical appliances such as an electric heater, toaster, geyser,
mosquito rackets etc.

ii.
It is used in the filament of the bulb to
make it glow in extreme heat.

iii.
It is also used in fuse used in our
domestic circuit to save us from dangers.

## 4 comments

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