Electrical Power
Kilowatt hours/watts
 

Objectives
Students Will learn
 About the concept of electrical power
About how to solve for power in a circuit
about use the use of kilowatt hours
about the use of kilowatt hours in real life

The Concept of
Electrical Power

      Electrical power is the product of voltage and current.   The equation for electrical power is as follows:

When the current { I }  in a circuit as a result of a voltage { V }
then the Electrical Power { P }  going to the circuit is equal to
P=IV
So that means that to solve for the power produced by a
circuit, you multiply the voltage of the circuit by the
amps or current of the circuit.

            Electrical power is noted in the unit of Watts and is noted as W in equations.  A Watt is equal to the product of an ampere on a volt.
 
 

The use of Electric power
In Real LIfe

The main use of electrical power is in the way that electrical companies charge for power.
They use the amount of power displayed in a set amount of time.  This means that Energy is equal to the power used multiplied by the amount of time it was used in.  Or...

Energy = Power(kw) X time(h)

The Electric company measure power in Kilowatts( kW ), or 1000 watts, and the time in hours( h ).  So the standard unit of power is Kilowatt hours( kWh ).    The way Electric companies charge you is per Kilowatt hour so the equation  for the cost would be

Total cost = Energy x Cost per unit

 

Sample Equations

1.   Circuit has is hooked up to a 9 volt battery and has a current of 2.5 Amps.  What   is the power used by the circuit.

                                    P= V x I
                                    P= (9v)(2.5 amps)
                                    P=22.5w

2.  A circuit has a current of 1.45 Amps and uses 10.9 watts.  How many volts does this circuit use?

                                    P= V x I
                                    V=P/I
                                    V = (10.9w)/(1.45 Amps)
                                    V= 7.517 volts

3. A circuit is hooked up to a 9 volt battery and uses 15 watts of power.  What is the current of the circuit

                                    P= V x I
                                    I= P/V
                                    I= (15 watts)/( 9 Volts)
                                    I= 1.667 amps

3.  A refrigerator runs at 230W it runs for 23 days how much energy does it use?

energy = P x T
energy = (230w/1000) x (23d x 24h)
energy = 0.23 kW x 552h
energy = 126.96 kWh

lets say that the company charges $0.11 for
each kWh  you use so what would the cost for
running this refrigerator.

Total cost = energy x cost per unit
Cost = 126.96 kWh x $0.11P/kWh
Cost = $13.97