### Electricity notes class 10th CBSE | Physics | Science

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

Rs  = R1  + R2  + R3.....

Given below is the formula for equivalent resistance in parallel connection

1/RS  = 1/R1  + 1/R2  + 1/R3.....

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 = I2R

P = V2/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 = I2Rt

Where H = Heat energy

I = Electric current

R = Resistance

t = Time

Ø  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 =V2t/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.

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