When it comes to the flow of electric current , all materials fall into two categories:
In all our activities we have used metal wires to make a circuit. Suppose we use a cotton thread instead of a metal wire to make a circuit. Do you think that the bulb will light up in such a circuit? What materials can be used in electric circuits so that the current can pass through them? Let us find out.
Disconnect the switch from the electric circuit you used to make an electric switch. This would leave you with two free ends of wires. Bring the free ends of the two wires close, to let them touch each other. Does the bulb light up? You can now use this arrangement to test whether any given material allows current to pass through it or not. Using a conduction tester you can test whether the bulb glows when the tester is in contact with a key.
Collect samples of different types of materials such as coins, cork, rubber, glass, keys, pins, plastic scale, wooden block, pencil lead, aluminium foil, candle, sewing needle, thermo Col, paper and pencil lead. One by one bring the free ends of the wires of your tester in contact with two ends of the samples you have collected . Make sure that the two wires do not touch each other while you are doing so. Does the bulb glow in each case?
Make a table in your notebook similar to Table.1, and record your observations.
|Object used in
place of the
What do you find? The bulb does not glow when the free ends of the wires are in contact with some of the materials you have tested. This means that these materials do not allow the electric current to pass through them. On the other hand, some materials allow electric current to pass through them, which is indicated by the glowing bulb. Materials which allow electric current to pass through them are conductors of electricity . These materials are made up of atoms whose electrons can move away freely.
Any material that does not allow electric current to pass through it is called Insulator.The rubber or plastic on an electrical cord provides an insulator for the wires. By covering the wires, the electricity cannot go through the rubber and is forced to follow the path on the aluminum or copper wires.
With the help of Table 12.1, name the materials that are conductors of electricity and also those which are insulators.
Conductors ______, ______, _________
Insulator _________, _______, ________
What do you conclude? Which materials are conductors and which are insulators? It now seems easy to understand why copper, aluminum and other metals are used for making wires.
Let us recall the activity in which we made an electric circuit with a switch . When the switch was in the open position, were the two drawing pins not connected with each other through the thermo Col sheet? But, thermo Col, you may have found is an insulator. What about the air between the gap? Since the bulb does not glow when there is only air in the gap between the drawing pins in your switch, it means that air is also an insulator.
Conductors and insulators are equally important for us. Switches, electrical plugs and sockets are made of conductors. On the other hand, rubber and plastics are used for covering electrical wires, plug tops, switches and other parts of electrical appliances, which people might touch.
Electricity will always take the shortest path to the ground. Your body is 60% water and that makes you a good conductor of electricity. If a power line has fallen on a tree and you touch the tree you become the path or conductor to the ground and could get electrocuted.Therefore, be careful when you handle an electrical appliance.
Water is a good conductor of electricity, but in its purest form, called distilled water, it acts as an insulator. Distilled water is, therefore, used in batteries as an insulator.
Materials that allow electric current to pass through them are called conductors.
Materials that do not allow electric current to pass through them are called insulators.
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