Transcript Watts.pptx

The Watt is the SI unit of Electrical Power.
It is the “work done” by electricity, and is a value of work
generated by 1 Amp flowing at a voltage of 1 Volt.
Therefore 1 Watt = 1 Volt multiplied by 1 Amp
Or W = V I
In mechanical terms, a Watt is the work required to move
an object at 1 meter per second against a force of 1
Newton.
W=VI
2
Now we know that Watts are a measurement of Electrical
Power, we can note their uses everywhere.
Such examples are lamps (light bulbs), motors and
heaters which all have an electrical rating in Watts.
The higher the wattage, the more electrical power the
item will consume.
One Kilowatt is One Thousand Watts, and is a typical
rating for electric motors.
1 Kilowatt (KW) = 1.34 Horsepower (Hp)
The consumption of Electricity is measured in KW/Hour.
This is the amount of electrical power used in a specific
hour.
3
Power and energy are frequently confused. Power is the rate at which
energy is generated and consumed.
For example, when a light bulb with a power rating of 100W is turned on for
one hour, the energy used is 100 watt-hours (W·h), 0.1 kilowatt-hour, this is
not the energy used to light the bulb, just the power consumed to keep the
bulb lit for that period .
This same amount of energy would light a 40-watt bulb for 2.5 hours, or a
50-watt bulb for 2 hours.
40 X 2.5 = 100 Watt hours and 50 X 2 = 100 Watt hours.
A power station would be rated in multiples of watts, but its annual energy
sales would be in multiples of watt-hours. A kilowatt-hour is the amount of
energy equivalent to a steady power of 1 kilowatt running for 1 hour, the
actual energy for this would be 3.6 Mega Joules.
4
A Simple
battery torch
Bulb = 6 Watt
As we know Power (P) = V x I, We can also work out that from
the triangle above, I =P/V and V = P/I
Therefore the torch above would generate I = P/V = 6/3
= 2 amps in the circuit above.
5
Looking at the 2 triangles above we can see that V= I X R
and P = V x I.
So we can rightly assume P = (I x R) x I which = I x I x R or
P=I R
Also R = V/I and V = P/I, so R = P/ I x I or P/I
and so on.
6
7
Power and Ohms law formulas are needed in a variety of
everyday uses by electrical engineers.
Examples of this include the calculation for over current and
fuse protection, calculation for the size of wiring to use for new
equipment, and for design and purchasing when you need the
maximum allowed value of equipment for a given installation.
8