CBSE Class 10 Science Chapter 12 Electricity Notes

Electric CIrcuit:-

A closed path through which electric current flows is called electric circuit.

Types of wires:

Neutral wires (black)
earth wires (green wire )
Live wire ( Red wire)

Electricity supplied to our house is 220 V 50 Hz, in A.C.(i.e. Alternating Current)

Some Important terms related to electric circuit

Charge
Current
Resistance
Voltage

Define Charge:-

It is defined as the particles (mainly negative charges) which are responsible for the flow o

electric current.

Formula Q= I t

Units- It has unit Coulomb (C)..

Current:-

It is defined as the flows of electric charges (mainly electrons) in the wire per unit time.

Formula-

Unit It has unit Ampere (A).

Define the unit of current (1 Ampere)

A current is said to be 1 ampere when one-coulomb charge flows through a wire in 1 sec.

1A=1 C / 1 sec

Resistance:-

It is defined as an opposition offers by a wire to flow of electric current.

Formula R=V/I.

It has unit Ohm.

Define the unit of resistance.

Resistance is said to be one ohm when a one-ampere current is passed through a wire due to the applied potential of one volt.

1 ohm = 1 volt / 1 ampere.

Voltage (potential difference )

It is defined as work done to move per unit charge from one point to another point against the potential.

formula V = W/ Q; V= I R

unit it has unit Volt (V).

Define one unit of voltage (1 V)

a voltage is said to be One volt when one joule of work is done to move a charge from one point to another point.

Formula

Some important symbols related to electric circuit

Some important points to remember about electricity:

The electric current always flows from positive to the negative terminal of a battery (means from higher potential to lower potential )
Ammeter: It is a device that is used to measure the electric current which is passing in the electric circuit. An ammeter is always used in series to the circuit from which we have to find the current.
Voltmeter:-It is a device that is used to measure the voltage or potential difference that is present across any device or resistance. The voltmeter is used in parallel connection across a device in a circuit.

Ohm's Law:-

According to the ohm.s law, the current flowing through a wire is directly proportional to the potential difference across its two ends at a constant temperature.

Let I am the current flowing in the circuit in which V potential difference is applied. Then according to the ohm's law, I a V

I = V / R

where

R- resistance offered by the wire.

V - Voltage or the potential difference is applied across the circuit

I - current following through the circuit.

Voltage, current graph of Ohm's Law:-i.e. V-I graph

The Graph will be a straight line which will show to us that there will be the linear change in the value of current with the potential. The graph is a straight line and inclined to the x-axis (or with the voltage axis.)

What is resistance? Write down the factors on which resistance depends.

Resistance is defined as hindrance or opposition offers to the flow of current by the wire.

Unit of resistance:-

It has a unit, Ohm.

Factors on which it resistance depends.

We know that the resistance of a wire depends on the following factors as follow

1. Resistance is directly proportional to the length of the wire. More is the length of the wire more will the resistance offers by the wire and vice-versa.

2. Resistance is inversely proportional to the area of a cross-section of the wire. More is the area of the wire lesser will be the resistance offers to the flow of current.

Combining these two equations we can write it as

Here ⍴ (rho) is the resistivity or a specific resistance of a wire. It does not change with the change in the area and length of the wire.

The resistivity of a material

The resistivity or Specific resistance is defined as the resistance offered per unit length and unit cross-sectional area when a known amount of voltage is applied.

Note:-

Resistivity is a constant quantity for a particular material and if we take a wire of 1-meter length and area of it 1 m²than the resistivity of a material is equal to the resistance of that material.
It is the characteristic of a wire that depends upon the type of the material.

Series and parallel connection or resistance:-

Series Combination:-

Two or more resistances are said to be connected in series connection. If the same current is flowing through them.

OR if two resistances are join end to end and having only one end common than also we can say that they are connected in the series combination.

Derivation:-

Consider three resistances are R₁, R_2, and R₃ three resistances connected in the series combination through which current (I) is passed and V₁, V_2, and V₃is the potential difference across R₁, R_2, and R_3.

_So,V=V₁+V₂ + V_{3 ____ (i)}

_{By ohm's law V =I R}

V₁ =I R₁

V₂ =I R₂

V₃ =I R₃

_{Take these equations as 2nd equation}

_{when we put equation 2nd in equation 1 then we will get,}

Parallel Combination:-

Two or more resistances are said to be connected in parallel connection. If the same potential difference across all the resistances but different amount of the current is flowing through them.

OR if two resistances are joined such that they are having both the end common than also we can say that they are connected in the parallel combination.

Derivation:-

_{Heating effect of the Electric current:-}

When an electric current is passed through bulb filament it gets hot and it glows and emitted light similarly when current is passing through a filament of electric iron. The iron becomes very hit and there is increase in the temperature which is called heating effect of the electric current.

Consider a circuit whose resistance is 'R' through which current is passing and having a potential difference 'V' and charge 'Q' is passing through circuit ,heat is produced that is

U=H=Q*V ________(1)

By the ohm's law, V= I R _______(2)

Q=i*t _________(3)

put these equations 2nd and 3rd in the equation 1st, we get

U= I²Rt

By multiplying and dividing R

H=U = I²R²t / R = I²Rt

= i*i*r*t

We know that V= iR

then U= H= V i t

Electric power:-

We know the rate of doing work is called power. In a similar way, the rate at which electric energy produced or consumed per unit time called is Electric power.

Formula

Units: It has a unit Watt or Joule per sec.

Joule's law of heating:-

According to joule's law of heating .when current is passed through any heating device (element) the heat is produced. The heat produced is directly proportional to the square of current passing through it.and it is directly proportional to the time for which the current is passing through a wire.

H=i²Rt

Units:- It has unit joule ( J ).

Electric Bulb:-

an electric bulb has a simple structure. It consists of a sealed glass bulb that has a tungsten filament connected to two electrical contacts. The bulbs us filled with an interactive gas like argon (Ar), nitrogen. To produce white light, the filament has to be heated to about 3000℃ by passing a current through it. Tungsten is used for the filament because its melting point is about 3400℃. The sealed glass bulb serves two purposes first, it protects the filament from oxidation and the effects of humidity. second, the small enclosed volume makes it easier to maintain the required temperature as without it loss of heat would be more.

Fuse:-

A fuse is a safety device that does not allow excessive current to flow through an electric circuit. It consists of a metallic wire of low melting point, fixed between two terminals of a fuse plug. A fuse is connected in series with an appliance. So, the current through the fuse as the same as the through the appliance. Of the current exceeds a safe value, the heat produced in the fuse wire causes it to melt immediately. This breaks the circuit preventing any damage to the device.

Related Topics:-

To Read Part 2 of these Notes.click on this link.

Electricity Class 10 Notes Has The Answer To Everything about Electricity.(Part-2)

CBSE Class 10 Science Chapter 12 Electricity Notes