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.

GRAMMAR REVIEW: Present, Past, Modals

ERROR ANALYSIS

CHECK THE SENTENCES. THERE IS A MISTAKE ON EACH OF THEM. PAY ATTENTION ON THE UNDERLINED WORDS. DECIDE THE MISTAKE & WRITE THE CORRECTION WORD/PHRASE ON YOUR ANSWER SHEET.

1.      

1.                  Although mathematics were never easy for him when he was younger, he’s glad he has chosen it as his major.

2.                  My supervisor promise that I will get a raise next year.

3.                  Work in factories are too boring, heavy and repetitive.

4.                  The first category of material is substances which provide an easy path for an electric current.

5.                  Under certain conditions semi-conductor allow a current to flow easily but under others it behaves as insulator.

6.                  What does the hardest thing you can do related to the job that you want?

7.                  The board of directors are deciding now who will get a promotion and who will be fired.

8.                  People usually wearing clothing for two basic purposes – warmth and decoration.

9.                  Why certain plants contain alkaloids remain a mistery, although botanists have formulated a number of theories to explain it.

10.               Arabic is Ali’s native language, but right now he speaks English.

11.              She actually could finished the work yesterday, but she didn’t.

12.              When I was a child, I can swim in Bengawan Solo River, but now it’s too polluted. So, I can’t swim there anymore.

13.              After working hard the whole day, you should going home and take a nap.

14.              A: I haven’t paid my electric bill.

            B: You’d better paying it soon otherwise your house will be dark.

15.              Again, the deadline will be push back for a third time.

16.              Workers from fifty years ago would not can recognize today workplace.

17.              Dr. Dixon was never be able to get over the loss of his first heart transplant patient.

18.              The Taj Mahal is must for tourists visiting India.

19.              I would rather read a book in the evening than visiting friends.

20.              There will be a test tomorrow. Let’s studying now.