Electrical Energy and Power
From the initial definition of POTENTIAL DIFFERENCE across two points in an Electrical circuit.
Also, we defined ELECTRIC CURRENT as the Quantity of charges moved in a circuit per unit time
From these two formula,
Therefore the work done or Electrical energy used up can be defined mathematically as;
From ohm’s Law V=IR
Also
ELECTRICAL POWER
The unit of Power is J/s = volt-Ampere or watt(w)
The power used by some Electrical devices are measured in horsepower
1 horsepower (h.p)= 0.75kw
KILOWATT-HOUR
The commercial power consumed is calculated in Kilowat-hour(kwh)
Most Distribution companies sell in kilowatt-hours.
How to convert your house Electrical used up to kilowatts-hour
If you have a bulb rated 60watt and this bulb is switch ON for 15min
The consumed Energy is 60watt-15mins
But 60watt = 0.06kilowatt
And 15mins =0.25 hour
The Energy used = 0.06kw x 0.25h = 0.015kwh
If the distribution company charge $1 for a kwh
The price for the consumed Energy = $0.015
KILOWATTHOUR in joules
1 kilowatthour = 1000w x( 60x60)s
J
Example
An Electric bulb is rated 240v 100watt. How much current is taken by the bulb ? if this bulb is ON for 15mns , what is the consumption in kwh ?
Solution
P=IV
100=I x240
In kilowatt-hour
100watt-15mins=0.1kw x 0.25h = 0.025kwh