NOTES PREPARED BY
ASHAQ HUSSAIN BHAT
TEACHER SCHOOL EDUCATION
JAMMU AND KASHMIR
ELECTRIC POWER
When an electric current flows through a conductor, electrical energy is used up and
we say that the current is doing work. We know that the rate of doing work is called
power, so electric power is the electrical work done per unit time. That is,
Power =Work done /Time taken
Power
Or P=W/t
Unit of Power :- Power is calculated by dividing work done by time taken. Now, the unit of
work is “joule" and that of time is "second". So, the unit of power is “joules per second".
This unit of power is called
watt. Thus, the SI unit of electric power is watt which is denoted by the letter W. The power of 1 watt is a rate of working of 1 joule per second that is
1watt=1joule/1Second
Actually, watt is a small unit, therefore, a bigger unit of electric power called kilowatt
It is used for commercial purposes that means
1 kilowatt = 1000 watts
or 1 kW = 1000 W
It should be noted that the symbol for watt is W and
that for 1 kilowatt is kw. When work is done, an equal
amount of energy is consumed. So, we can also say that
electric power is the rate at which electrical energy is
consumed. In other words, electric power is the electrical
energy consumed per second.
COMMERCIAL UNIT OF ELECTRIC ENERGY
The commercial unit of electric energy is called kilowatt hour (kWh) or Board of Trade Unit (BOTO) or Unit in brief. The electric energy consumed when an electric appliance of power one kilowatt works for one hour is called one kilowatt hour.
1 kWh = 1 kW X1 h
= (1000 W) x (3600 s) = 1000 (J/s) × (3600 s)
(1W=1J/s)
= 3.6 10 J = 3.6 MJ
1 kWh = 3.6 MJ
We know that electric energy, W = VI t
If V is in volt, I is in ampere and t is in hour, then electric energy (W) is in watt hour (Wh), i.e.,
1 Wh = 1 volt x 1 ampere x 1 hour
Thus electric energy,
W (in kWh)=V( volt x 1(ampere) x + (hour)/1000
Practical applications of leading ethet of current.
The heating effect of current has but many useful practical applications such as
1:-An electric iron, electric geyser, electric toaster, electric oven, electric kettle, some of the familiar devices based on joule heating, or heating effect of current
2:-An electric bulb is used to provide light by heating its filament
3:-An electric fuse used as a safety device in electric circuits is important application of joule heating cheating effect of current
Why Tungsten metal is used for Making the filament of conventional electric bulb
Tungsten metal is used for making the filaments of electric bulbs because it has a very high melting point (of 3380°C). Due to its very high melting point, the tungsten filament can be kept white-hot without melting away. The other properties of tungsten which make it suitable for making filaments of electric bulbs are its high flexibility and low rate of evaporation at high Argon or Nitrogen
temperature. Please note that when the tungsten filament Glass of an electric bulb becomes white-hot and glows to emit light, then its temperature is about 2500°C ! If air is present in an electric bulb, then the extremely hot tungsten filament would burn up quickly in the current. Air So, the electric bulb is filled with The gases like argon and nitrogen Or both for the prolong life of the filament of the electric bulb..
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