Electricity and Electric meter

Electricity

Electrical energy can be easily converted into heat, light and other forms of energy. During such conversions the quantity of energy neither increases nor decreases. This phenomenon is called 'conservation of energy'. The effects of electric current are used for different purposes. Make a list of the applications of electricity that you see in your surroundings. Mention the energy transformation involved in each application.

Do you know ?

Gilbart was the first person to pur forward the idea of Earth as a magnet. To test this ieea he prepared a small sphere our of magnetite ore and called it Terrella or little earth. When a magnetic needle was kept on terrella. It always used to come to rest in a particular direction. On this basis he declared that there was only one difference between his Terrella and Earth. “The Earth is bigger, my Terrella is small”. It is a wonder how magnetism exists even at the high temperature in the interior of Earth.

Units of measurement of electriity in the S.I. System is 'Joule'. Multiple unit called kilojoule is also used. One kilojoule is equal to one thousand joules.

1 kJ = 1000J

Electric power

Electricity can heat a coil of wire, run machines and make bulbs emit light. All these prove that electricity can do work. Electric power is the rate at which electricity is made use of.

Electric Power = Electrical energy used / time

If a device uses E joules of current in 't' seconds, then power (P) is expressed as follows.

P = E / t

Unit of electric power : The S.I. Unit of electric power is watt. If a device uses electricity at the rate of 1 joule per second. Then its power is a watt.

I watt = 1 joule / second

1 w = 1 J/s

Watt is a small unit. Hence a multiple unit, kilowatt is used. One kilowatt is equal to one thousand watts.

1 kW = 1000 W

= 1000 J / s

Example : If a bulb uses 1500 joules of current in 25 seconds, what is its power ?

P= E / t

= 1500 / 25

= 60 watt.

Electric Meter

Practical unit of electricity.

Joule and kilojoule are not conventent units for practical purposes. Therefore kilowatt-hour (kWh) unit is used to measure electricity for commercial purposes. Electricity that we use in factories and our homes is measured with this unit. Let us now understand what one kilowatt hour means.

Let us assume that we are using 1000 Joules of electricity every second. If we continue to use electricity at the same rate for one hour. 


The quantity of electricity used is one kilowatt-hour. One kilowatt-hour is one unit of current.

1 kilowatt-hour = 1 kilowatt x 1 hour.

= 1000 watt x 1 hour

= 000 J/s x 3600 s

= 360000 joules.

Effects of electric current

The flow of current can causes the following effects on substances.

1.   magnetif effect.

2.   chemical effect.

3.   heating effect.

Magnetic effect of electric current

Whenever an electric current flows through a conductor a magnetic field is created around the current-carrying conductor. This was discovered by Henry Christian Oersted. Magnetism and electricity go hand in hand. One does not exist without the other. We now know that magnetic property of some substances is due to the movement of electric charges in their atoms.

Chemical effect of electric current

Whenever an electric current flows through some solutions, they undergo chemical changes. This is called the chemical effect of electric current. Electric current does not flow through some substances. They are insulators. It flows through some substances only when they are in liquied form or in solutions : Sodium chloride. Copper sulphate, suphuric acid etc. Such compounds are called electrolytes. Those compounds through which the electric current does not pass either in aqueous solution or in liquid form are called non-electrolytes : sugar, glucose, castor oil etc.

Heating effect of electic current : 
Whenever an electric current flows through a wire. A small part of electrical energy is converted into heat energy. This is called heating effect of electric current. The wires made of certain substances produce relatively more heat than others of the same dimension. This effect of electric current is utilised in appliances like electric stove, boiler, electric fuse, electric iron, electric bulb, water heater etc.