Electrical energy and electrical powerCopy

Learning Objectives

• Understand that electric circuits transfer energy from the battery or power source to the circuit components then into the surroundings
• Recall and use the equations P = IV and E = IVt

Contents to learn

Electrical energy
Whenever there is an electric current in a conductor, the conductor gets heated up. It shows that energy is obtained from the electric current.

Formula for electrical energy
In the above figure, when the current passe through R, heat is produced across the resistor. By definition

V = W / Q

W = VQ

i.e. W, work is obtained when a charge ‘Q’ flows between two points maintained at a potential diference of V. Across a conductor this work may appear as heat energy as a result the temperature of the conductor rises.

electric current is the rate of flow of charge if current 1 amp, flows for ‘t’ seconds between two poits then the charge (Q = It) flows between those ponits in time ‘t’, then amount of energy obtained by the current during time ‘t’ is

W = QV = VIt

If a current of I(ampere) is flowing through a resistor R, ohms, whose ends are maintained at potential difference V(volts) then by Ohm’s law

V = IR

Hence W = VIt

or W = I2Rt

The electrical energy W in the resistor is dissipated as heat energy.

Electrical Power
Power is the rate of doing work. Similarly amount of energy obtained from an electric current in unit time is called electric power i.e.

Power = Work / Time

Formulae for electrical power
p = W / t ……………………………………(1)

Since W = VIt

Therefore P = VIt / t

So P = VI …………………………………….(2)

or P = (IR)I since V = IR

or P = I2R…………………………………….(3)

Since P = VI

or P = V(V/R)

or P = V2/R ………………………………….(4)

The above four equations can be used to determine the electical power depending upon the given infomations

When V is in volts, I is in amperes and R is in ohms, then power is in watts. Following units of power are in common use

1 Kilo Watt = 1KW = 1000 W

1 horse power = 746 W