17. Write the description of the following diagram. Does it answer the following questions?

1. What is the diagram of?

2. What does it consist of in terms of blocks?

3. How are the blocks connected?

4. What is the function of each block?

Fig. 3

Lesson 3. Batteries

Lead-in.

1. Answer these questions. 1. What do you know about batteries? 2. Over twenty billion batteries are sold every year. – Why do you think this is so? 3. List some of the things you use which contain batteries.

Reading and Vocabulary.

2. You are going to read the text about batteries. Make sure you know these words and expressions.

to power battery bank standby telephone exchanges computer data centre multiple source household and industrial appliances estimate to generate

annual growth advantages and disadvantages primary (disposable) battery to discard secondary (rechargeable) battery negative electrode positive electrode solution EMF = electromotive force cordless

3. Read the information about batteries and complete the table of differences between the two types of cells.

Batteries

Everyone knows what a battery is: usually it’s one of those little tubes that you put in your walkman or your torch so that you can have music or light where you go. It’s portable electricity.

In fact, batteries come in many shapes and sizes. They range from the button-sized ones which keep your watch and hearing aids going for more than a year to the heavy batteries which can power submarines or to battery banks the size of rooms that provide standby power for telephone exchanges and computer data centers.

Strictly, a battery is a collection of multiple electrochemical cells, but in popular usage battery often refers to a single cell. For example, a 1.5 volt AAA battery is a single 1.5 volt cell, and a 9 volt battery has 6 1.5 volt cells in series. The first electrochemical cell was developed by the Italian physicist Alessandro Volta in 1792 and in 1800 he invented the first battery, a ‘pile’ of many cells in series (‘voltaic pile’).

Since the invention of the first battery by Alessandro Volta, batteries have become a common power source for many household and industrial appliances. According to a 2005 estimate, the worldwide battery industry generates US $ 48 billion in sales each year, with 6 % annual growth.

Batteries are classified into two main categories. Each type has some advantages and disadvantages, but both kinds change chemical energy into electricity. Primary batteries (disposable batteries) are designed to be used once and discarded. They are thrown away when the chemicals they contain are used up. Secondary batteries (rechargeable batteries) are designed to be recharged and used multiple times.

The commonest and cheapest kind of primary cell is the Zinc-carbon cell. It consists of a zinc can which contains two chemicals. The zinc is the negative electrode. One of the chemicals, manganese dioxide, forms the positive electrode. The electrolyte is a solution of ammonium chloride. The electromotive force is 1.5V. Millions of cells like this are used every year in clocks, torches, tape recorders and remote controls.

Secondary batteries can be used again and again. The NiCad cell fits this description. It’s a secondary cell with a nickel positive electrode and a cadmium negative electrode. Ni for nickel, Cad for cadmium – NiCad. The electrolyte is potassium hydroxide. It has an EMF of 1.2V. NiCad cells are more expensive, but they can be recharged hundreds of times. They are used in many cordless appliances such as mobile phones.

	Zinc-carbon cell	NiCad cell
Type of cell
Positive electrode
Negative electrode
Electrolyte
EMF
Example of use