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

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