Electricity Class 10 full notes

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Electricity

 

Electricity is a branch of physics in which we study about the charges at rest or in motion. Electricity is further divided in two branches - Electrostatics and Current Electricity. 

 

Electrostatics : Electrostatics is a branch of electricity in which we study about the charges at rest. 

 

Current Electricity : Current Electricity is a branch of electricity in which we study about the charges in motion ( about Electric current and its effects). 

 

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Concepts:

 

• Every atom as a whole is electrically neutral. Its total positive charge is equal to its total negative charge. Charges are produced by loss or gain of electrons.

 

• Charges in motion and Electric Current: Charges in motion constitutes current electricity. The Electric current is defined as the rate of flow of charges through a cross section of a conductor. The charges flow from higher potential to lower potential. By convention, the direction of electric current is taken as the flow of positive charges. Negative charges flow from lower potential to higher potential.

 

• Electric Field: The region or space around a charge upto which a force of attraction or repulsion can be experienced by any other charge, is known as electric field. 

 

• Electric potential: The Electric potential of a point in an electric field is defined as the amount of work done in bringing a unit positive charge from infinity to that point along any arbitrary path.

 

• A positive charge in an electric field moves from higher potential to lower potential, while a negative charge moves from lower potential to higher potential.

 

• Potential difference: The amount of work done in moving a unit positive charge from a point of lower potential to a point of higher potential between the two points.

 

Ohm's law: 

According to Ohm's law,  the current flowing through a metallic conductor is proportional to the potential difference applied between its ends, provided its temperature remains constant. 

  

     i. e.      V ∝ I

     or        V = R I       …… ….. (1) 

 

where R is a constant of proportionality and it is called the resistance of the conductor. 

 

Resistance: The property by virtue of which a conductor opposes the flow of charge in it is known as resistance. The resistance of a conductor depends directly on its length, inversely on its area of cross-section and also on the material of the conductor.

 

Resistors in series

 

(i) Current in each resistor is the same.

(ii) Potential difference across each resistor is different and is proportional to the resistance.

(iii) Equivalent resistance of the arrangement is

                        

                      R=R1+R2+R3

Effective resistance is greater than any individual resistance.

 

(iv) If 'n' wires, each of resistance R, are Connected in series, the effective resistance is nR.

 

Resistors in parallel

 

(i) Currents in the resistors are in proportion to the reciprocals of resistances.

(ii) Potential difference across each resistor is the same.

 

(iii) Equivalent resistance of the arrangement is 

  

                               1/R=1/R1+1/R2+1/R3

Effective resistance is less than any individual resistance.

 

(iv) If 'n' wires, each of resistance R, are connected in parallel, the equivalent resistance is R/n.

 

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Heating effects of electric current: The heat (H) produced is proportional to the square of the current, the resistance of the wire and the time for which the current flows.

 

i.e.       H ∝ I2

            H ∝ R

            H ∝ t

 

Hence,       H ∝  I2 R t

 

The constant for proportionality here is found to be 1.

 

Hence        H =  I2 R t      ….. ….. …. (2) 

 

Also           H =  V I t

 

or               H = V2 t / R

 

Electric Power : Power is defined as the rate of doing work or the rate at which energy is produced or consumed. The electrical energy produced or consumed per unit time is called electrical power.

It is denoted by P. 

 

                     Power = Energy / time

 

                      P = H /t    …… ……. . …. .. ( H is energy given by equation 2) 

 

Or                 P = I2 R = V I =  V2 / R

         its SI unit is watt ( W). 

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