VII. Choose the correct variant:

1. A resistor is used a) to reduce the value of cur­rent, b) to store electric charges.

2. The value of a fixed resistor is a) variable, b) fixed.

3. Devices used to regulate the value of current are called a) capacitors, b) rheostats.

4. In a wire-wound device the wire has a) low resist­ance, b) high resistance.

5. Different loads operate a) at a constant voltage, b) at a variable voltage.

6. The value of resistance between the terminals of a rheostat a) varies, b) does not vary.

VIII. Translate the text. Use a dictionary: About the First Incandescent Lamp

The first incandescent lamp for practical use was produced in Russia, in 1873 by the great Russian scien­tist Alexander Lodygin. In his lamp he fixed a small carbon rod of about 2 mm in diameter between two copper conductors. In order to protect the lamp from burning through, the lamp's air had been evacuated. Vacuum at the time being far from perfect, this first lamp was short-lived. Its life was measured in hours.

In 1890 Lodygin made his first lamps with a metal filament using metals with high melting points, such as tungsten, molybdenum, osmium.

A few years later Thomas Edison, an American in­ventor, improved lamps with a metal filament. He used the lamp holder, the switch and some other elements of the lighting network.

Today the filament of the incandescent lamp is twisted into a spiral. The melting point of tungsten being 3,300°, it can be heated to 3,000°. At this temper­ature, however, tungsten begins to evaporate. In order to avoid evaporation of tungsten, today lamps are filled with chemically inert gas, i.e. argon or cripton.

In a gas-filled incandescent lamp the ends of a filament are connected to the two wires passing through the bulb and attached to the metal base. One of the wires is attached to the base and the other - to the base contact insulated from the base.

Industry manufactures incandescent lamps for 220 and 127 V (for lighting networks), 50 V (for railway wagons), 12 and 6 V (for motor cars), 3.5 and 2.5 V (for pocket torches).

Unit nine

Exercises

I. Translate the following words:

equipment, quartz, sand, rating, case, link, fault; sim­ple, faulty, direct, alternating; to serve, to base, to place

II. Translate the words. Mind the prefixes:

to place - to displace - displacement; to charge - to dis­charge; to move - to remove; to equip - to reequip; mov­able - removable

III. Translate the word-combinations in writing:

quartz-sand fuse, fusible link, faulty fusible element, faulty protection device

IV. Fill in the verbs "to serve", "to reequip", "to replace":

1. The lab should be … with modern equipment.

2. This fuse cannot ... as a protective element since it is faulty. It should be ... with a new fuse.

V. Translate the sentences. Mind "both ... and", "in case", "up to":

1. Both solid and gaseous insulators are in use now­adays. 2. In case an element gets open it should be replaced by a new one. 3. Capacitors of extremely high capacity (up to 1000 mF) are produced nowadays.