Electric Magnet

Making a Magnet by Electric method 

Electromagnet making process

Electronagnet

Electrical method

Wind a good length of insulated copper wire around a steel bar which is to be magnetised. Connect the ends of the wire to the poles of a battery. When the electric current passes through the copper wire the steel bar becomes a magnet. (fig). If a soft iron bar is used. It becomes a strong magnet temporarily. It loses its magnetism as soon as the current in the copper wire is switched off. Such temporary magnets are called electromagnets.

Electric Magnet:-
An electromagnet is a device in which magnetism is produced by an electric current.
British electrician, William Sturgeon invented the electromagnet in 1825. The first electromagnet was a horseshoe-shaped piece of iron that was wrapped with a loosely wound coil of several turns. When a current was passed through the coil; the electromagnet became magnetized and when the current was stopped the coil was de-magnetized. Sturgeon displayed its power by lifting nine pounds with a seven-ounce piece of iron wrapped with wires through which the current of a single cell battery was sent.
Sturgeon could regulate his electromagnet; this was the beginning of using electrical energy for making useful and controllable machines and laid the foundations for large-scale electronic communications. Five year later an inventor called Joseph Henry - made a far more powerful version of the electromagnet. American, Joseph Henry(1797-1878), demonstrated the potential of Sturgeon's device for long distance communication by sending an electronic current over one mile of wire to activate an electromagnet which caused a bell to strike. Thus the electric telegraph was born.

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.

Electric Fuse

Fuse

1.15       Electric fuse

Fuse is a protective device which works on the heating effect of electric current. It is a wire made up of an alloy of lead and tin. This alloy has high resistance and low melting point. Fuse is kept in a ceramic box at the beginning of an electric circuit. (fig.)

Electric circuits are designed to carry electric current of a definite strength. If the strength of electric current crosses the safe level, the circuit and the instruments in the circuit may get damaged. In such situations the fuse-wire provides the neede protection. Fuse-wire melts and breaks the circuit as soon as the strength of electric current in the circuit crosses the safe level and thus prevents possible damage.

Electric bulb : 
The bulbs that we use function on the basis of heating effect of electric current. A tungsten filament in the form of a coil is mounted on two copper leads in the bulb. When electric current is passed through the coil it heats up and emits light. Nitrogen is filled in the bulb to give it a long life. 

Activity : 

Make a list of electrical gadgets used in your house. Find out the power of each of them.