Difference between Electric power and Electric energy
Electric power
1.) Electric power is defined as the rate of dissipation of electric energy or rate of doing work by the charges in an electric field.
2.) If conductor of resistance ‘R’ carries current ‘I’ when connected, across cell of p.d. ‘V’ for time ‘t’ then,
Electric power, P = W/t or P = W.t
∴P = V.I or P = I2 R (by Ohm^’ s law, V = I.R
3) SI unit of power is named after Sir James Watt as watt (W)
4) Electric power generally measured in larger scale, hence the preferred units of power are
1 kilowatt= 1000 watt
1 horsepower (1 hp) = 746 watt
5) By knowing the power of electric appliances, one can find how much current is required by the object to function.
Electric Energy
1.) Electric energy is the amount of energy spent or consumed by given electrical appliance in given time. It is product of the power of appliance and the time for which the instrument is working.
2.) If an appliance has power ‘P’ and works for ‘t’ then the electric energy consumed by the appliance is given as,
Electric energy, E = P × t
∴ P = V.I or P = I^2 R (by Ohm^’ s law,V = I.R)
∴ Electric energy, E = V × I × t
3) SI unit of electric energy is joule-sec.
4) When we use any electric instrument of power rating 1000 watt for 1 hour then the consumption of electric energy is read as 1 unit.
1 unit of electric energy = 1000 watt × 1 hour
= 1 kW. h
= 1000 ×3600 watt. second
= 3.6 ×106 J
5) When we spend 3.6 ×106 J of electric energy, electricity board charges us for 1 unit. On this basis the by calculating total power consumption during the month, electricity bills are to be generated.