In this article, we will read about electrical energy which is related to the book NCERT chapter 3 Physics Class 12. Electrical energy is energy that can be converted into other forms, such as heat, light, mechanical energy, etc., and vice versa. Electrical energy is used to drive household appliances and industrial equipment.
Definition of Electrical Energy
Electrical energy is the energy carried by electric current or stored in electric fields. It is measured in joules (J).
(or)
Electrical energy is the energy caused by the movement of electric charge through a conductor, producing work and heat.
(or)
The total work done by the source of EMF in maintaining electric energy for a given time is called electric energy in the circuit.
If potential difference V is applied across the ends of a wire, teh work done by the EMF source in moving a charge q from one point to another is given by the electrical energy is equal to work done
W = q V
By substituting the value of voltage from Ohm's law V = R I
W = q (IR) `{\because V = R I}`
W = (I t) (IR) `{\because q = I t}`
`W = I^2 R t`
`W = \frac {V^2}{R} t`
This work is stored in the form of electrical energy.
S.I. unit of electric energy is Joule
`1 J = 1 W \times s`
The commercial unit of electric energy is a kilowatt hour of the Board of Trade (B. T. O.) unit or electric unit.
1 kilowatt hour = 1 electric unit
1 kilowatt hour = 1 kilowatt `\times` 1 hour
1 kilowatt hour = 1000 watt `\times` 3600 s
`1 K W H = 3.6 \times 10^6 J`
Important Point
Comparing work and heat by using Joule's law
`W = J H`
`H = \frac {W}{J}`
`H = \frac {V I t}{J}`
`H = \frac {I^2 R t}{J}`
`H = \frac {V^2 t}{R J}`
Where H is generating heat, J = Joule's mechanical equivalent
`J = 4.2 \frac {J}{Cal}`
Electrical Power
The rate of work done by the source of EMF in a circuit is known as electric power.
(or)
Electric energy consumed per unit time interval is known as electric power. It is denoted by P.
If a current I flows through a circuit for time t then the power of the electric circuit is
`P = \frac{W}{t}`
`P = \frac{V I t}{t}`
`P = V I`
`P = (RI) I`
`P = I^2 R`
`P = \frac{V^2}{R}`
S.I. unit of electric power is watt
`P = \frac{W}{t}`
`1 W = \frac{1 J}{1 s}`
Generally, electric power is measured in kilowatts or megawatts.
Horsepower is a practical unit of power
`1 H P= 786 W`
We use cables for the transmission of power from the power station to houses and these cables have resistance. Due to this resistance power is wasted in the form of heat.
Power is an electric circuit
`P = V I`
`P = I^2 R`
`I = \frac{P}{V}`
The power wasted in transmission cables is
`P_c = I^2 R_c`
`P_c = \frac {I^2 R_c}{V^2}`
Thus, the power wasted in cables is inversely proportional to the square of voltage. Hence to minimize power loss, electric power is transmitted to distant places at high voltage and low currents.
These voltages are stepped down by the transformers before supplying to homes and factories.
Methods of minimizing heat loss during power transmission
`\star` Increase Voltage, Decrease Current.
`\star` Use Conductors with Low Resistance.
`\star` Improve Cable Design.
`\star` Optimize Transmission Path.
`\star` Regular Maintenance.
Numerical Question
When a bulb of 220 V and 100 W is connected by the source of 110 V then find the power consumption by the bulb. (Ans: 25 W)
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