02/07/2021

Power & Energy

Power

  • It is defined as the rate of doing work.

OR

  • It is rate at which electrical energy is consumed or dissipated.
  • If W is electric energy consumed in a circuit for a given time, the power

        P = W / t

  • Let, the electric energy supplied by a current source for a given time t is

       W = VQ

From equation ( 1 ) and ( 2 )

  • P = VQ / t …… ( 3 )
  • But I = Q / t …… ( 4 )

From equation ( 3 ) and ( 4 )

  • P = VI

According to ohm’s law V = IR

  • P = ( IR )R = I2R                           ( As V = IR )

According to ohm’s law I = V / R

  • P = VI = V ( V / R ) = V2 / R

Equation of Power

VI

I2R

V2 / R

 

The SI unit of power is watt.

Watt = Volt × Ampere

Electrical Energy

  • It is defined as the amount of energy consumed in an electrical circuit for a given time. 
  • The electrical energy not only depends upon electrical power but also on the time for which electrical power is supplied.
  • Electrical energy = Power × Time
  • Unit of electrical energy = Watt – Second

Kilo watt hour

  • The commercial unit of electrical energy is kilo watt hour ( kWh )/
  • One Unit = One kWh

                  = 103 × Watt × 3600 second

                  = 3.6 × 106 Watt second

                  = 3.6 × 106 Joule

Example

How many units are consumed by a lamp of 100 W if it will turn on for twenty hour.

Solution

Rating of lamp = 100 W

Twenty hour

1 kWh = One unit

Number of units consumed by lamp = 100 × 20

                                                                 = 2000 Wh

                                                                = 2 kWh

                                                                = 2 Unit

You may also like :

Load dispatch center

Compare class A, class B & class C Amplifier

Rectifier efficiency and Power efficiency

What do you mean by drift and drift velocity?

 


No comments:

Post a Comment