Vocabulary

8. Choose the correct spelling of these words and translate them:

diode diod	p-n juction p-n junction	anod anode	foward bais forward bias	reverse voltage revers voltag
cathode catode	curent ratin current rating	lead laed	cercuit circuit	threshold treshold

Speaking

9. Work in pairs, choose one of the following questions and discuss it.

1. What is the connection between diodes and semiconductors?

2. How would you assess the importance of diodes?

3. Are vacuum tube diodes still used or are they totally replaced by semiconductors?

2. Creating a p-n junction

Start here

1. Read the text below. Match the descriptions 1- 3 with the diagrams a-c in Fig. 2.5. Put the descriptions 1-3 in logical order. Indicate the n-type and p-type regions, holes and electrons, reverse and forward bias.

a)

b)

c)

Fig. 2.5. How a p-n junction works.

A diode is a two-terminal device, having two active electrodes, between which it allows the transfer of current in one direction only. Diodes are known for their unidirectional current property, wherein, the electric current is allowed to flow in one direction.

1. Suppose you connect a battery to this little p-type/n-type junction. What will happen? It depends which way the battery is connected. If you put it so that the battery's negative terminal joins the n-type silicon, and the battery's positive terminal joins the p-type silicon, the depletion zone shrinks drastically. Electrons and holes move across the junction in opposite directions and current flows. This is called forward-bias.

2. However, if you reverse the current, all that happens is that the depletion zone gets wider. All the holes push up toward one end, all the electrons push up to the other end, and no current flows at all. This is called reverse-bias.

3. Interesting things happen when you start putting p-type and n-type silicon together. Suppose you join a piece of n-type silicon (with slightly too many electrons) to a piece of p-type silicon (with slightly too few). What will happen? Some of the extra electrons in the n-type will nip across the join (which is called a junction) into the holes in the p-type so, either side of the junction, we'll get normal silicon forming again with neither too many nor too few electrons in it. Since ordinary silicon doesn't conduct electricity, nor does this junction. Effectively it becomes a barrier between the n-type and p-type silicon and we call it a depletion zone because it contains no free electrons or holes.

That's how an ordinary diode works and why it allows an electric current to flow through it only one way. Think of a diode as an electrical one-way street.

Grammar

2. Study the sentences below and pay attention to the underlined verb forms in italics.

I am an English teacher. I am teaching English now.

What are you? What are you doing now?

You are students. You are studying English now. You are listening to me.

Aren’t you?

This is Andrew. He is a future electronics engineer. He is learning about diodes at this moment.

That is Helen. She is learning English Grammar.

What are we doing? What are they doing?

Answer the following questions:

1. What are these verb forms?

2. am, is, are. What verb has such forms?

3. teaching, doing, studying, listening, learning. What do these verb forms have in common?

4. What grammatical notion is it? Is it a tense? What tense is it?

It is the Present Continuous or Present Progressive Tense.

3. How do we form sentences in the Present Continuous? Complete the table.

   Positive	Negative	Interrogative
   Subject + am, is, are+ Verb + ing.	Subject + am, is, are+ not Verb + ing.	Am, is, are + Subject+Verb + ing?
   I am teaching. You are studying. He She It We They	I am not studying. You are not teaching.	Am I studying? Are you teaching?

4. So, now we can form the Present Continuous. But when do we use the Present Continuous? Study the following table and give your own examples.

Actions are happening…	Examples
now right now at the moment of speaking at this very moment	I am teaching English now. You are not learning German right now, because this is an English class. At this very moment you are studying the Present Continuous.
around now around the moment of speaking currently, for longer actions in progress	He is studying to become an electronics engineer. Are you working on any special projects at work? Elizabeth is currently writing a children’s book. They are working hard to earn money.
this week, month, year these days, for temporary actions	I’m riding a bike to get to work because my car is broken. Helen is studying really hard for her exams this month. We aren't working hard these days.
tonight tomorrow next week, month, year, for future arrangements and plans	I am going to the theatre tonight. Polly is coming for dinner tomorrow. They are eating at a restaurant next week. He is flying to Rome in September. We are meeting our friends in the evening.
always constatly continually, for irritating repeated actions	She is continually complaining about everything! John is always asking stupid questions! You are constantly coming to class late!

5. Make a presentation on the topic: “Types of diodes”. You may present all types of diodes, or two of them to compare, or just the only one. Use the information in the table to help you.

How do I start?	You could grab your audience's attention by starting with a question or a challenging statement. Use pictures or objects. So, how much do you know about ...? Have you ever asked yourself why ...? What I'm going to tell you about today will change the way you think about... Pass around the picture/object. What do you think it is?
How do I organize the presentation?	Make it short. Write down the points you want to make, edit them, then decide which order you are going to make them in. Introduce each point with an expression from the list below. The first/key thing to say about _________ is... The main point to make about _________ is… What you really need to know about__________ is ... Now let's look at... Let's turn to/move on to ... Another interesting thing to say about__________ is ... Finally, I'd like to say a few words about...
What do I say?	After introducing the point, add information briefly in two, three, or, at the most, four sentences. Use markers like the ones below to construct long, well-balanced sentences. Anyway ...; Naturally ...; Of course ... Similarly ... ; Surprisingly …; Remarkably ... Despite ...; However ...; Although ...; Whereas ... Consequently ...; In addition ...; Moreover...; Furthermore ... Incidentally...; By the way...; It's worth noting that...
How do I finish?	Conclude the presentation by briefly summarizing what you have said, or the points you have made. You could end by asking for comments or questions. In conclusion...; To sum up... So, remember that……..is all about ……., and... So, there are three things to remember about… Does anybody have any questions?