CONDUCTORS, INSULATORS AND SEMICONDUCTORS

 I. Reading Comprehension

If we connect a battery across a body, there is a movement of free electrons towards the positive end. This movement of electrons is an electric current. All materials can be classified into three groups according to how readily they permit an electric current to flow. These are : Conductors, Insulators, and Semiconductors.

            In the first category are substances which provide an easy path for an electric current. All metals are conductors, however some metals do not conduct well. Manganin, for example is a poor conductor. Copper is a good conductor, therefore it is widely used for cables. A non metal which conducts well is carbon. Salt water is an example of a liquid conductor.

            A material which does not easily release electrons is called an insulator. Rubber, nylon, porcelain and air are all insulators. There are no perfect insulators. All insulators will allow some flow of electrons, however this can usually be ignored because the flow they permit is so small.

            Semiconductors are midway between conductors and insulators. Under certain conditions they allow a current to flow easily but under others they behave as insulators. Germanium and silicon are semiconductors. Mixtures of certain metallic oxides also act as semiconductors. These are known as thermistors. The resistance of thermistors falls rapidly as their temperature rises, They are therefore used in temperature sensing devices.

Answer the questions !

  

1.            What is electric current ?

2.            How is the flow of electrons ?

3.            What is the consideration to classify electrically all materials ?

4.            Why is copper a good conductor ?

5.            Why is rubber an insulator ?

6.            Why aren’t there no perfect insulators ?

7.            What is semiconductor ?

8.            Mention several examples of semiconductors !

9.            What are thermistors ?

10.        When do thermistors behave as insulators ?

 

 Fill the blank spaces based on the text with appropriate verbs!

1.            If a battery …………… across a body, there will be an electric current.

2.            Free electrons …………….. towards the positive end.

3.            We can ……………. all materials into three groups.

4.            An electric current ………………… an easy path by conductors.

5.            Manganin cannot  ……………….. well.

6.            Cables usually …………………... of copper.

7.            Although non metal, carbon ………………… electric current well.

8.            Electrons of insulators cannot ……………………. easily.

9.            If the flow of electrons is so small, it can ……………………

10.        Semiconductors sometimes ………………….. as insulators, sometimes as conductors.