3. Answer the questions.

1. What is the difference between such metals as silver, nickel and rubber?

2. What metal is a good conductor and why?

3. What materials may be insulators and why?

4. What four physical factors do you know?

5. What do you know about Ohm’s law?

4. Are the following sentences True or False?

1. Such metals as silver and copper have many electrons flying aimlessly.

2. Copper is the worst conductor of electric current.

3. Iron is a fair conductor.

4. Silver is a good insulator and glass is a good conductor.

5. Silver has the biggest resistance to current flow.

6. The unit of measurement of resistance is the amperes.

7. The current in amperes is equal to the potential difference in volts divided by the resistance in ohms.

5. Match the words with the meanings.

   aimlessly at high rate free electrons copper wire electric current ability measurement practical purpose electric circuit

   электрическая схема способность практическая цель на высокой скорости медный провод бесцельно электрический ток свободные электроны измерение

6. Render the text into English.

Электрическое сопротивление – физическая величина, характеризующая свойства проводника и равная отношению напряжения на концах проводника к силе электрического тока, протекающему по нему.

Высокая электропроводимость металлов связана с тем, что в них имеется громадное количество носителей тока – электронов проводимости, образующихся из валентных электронов атомов металла, которые не принадлежат определенному атому. Электрический ток в металле возникает под действием внешнего электрического поля, которое вызывает упорядоченное движение электронов. Движущиеся под действием поля электроны рассеиваются на неоднородностях ионной решетки. При этом электроны теряют импульс, а энергия их движения преобразуется во внутреннюю энергию кристаллической решетки, что и приводит к нагреванию проводника при прохождении по нему электрического тока.

7. Give the summary of the text.

The electrical resistance of an object is a measure of its opposition to the passage of a steady electrical current. An object of uniform cross section will have a resistance proportional to its length and inversely proportional to its cross-sectional area, and proportional to the resistivity of the material.

A metal consists of a lattice of atoms, each with a shell of electrons. This can also be known as a positive ionic lattice. The outer electrons are free to dissociate from their parent atoms and travel through the lattice, creating a ‘sea’ of electrons, making the metal a conductor. When an electrical potential difference (a voltage) is applied across the metal, the electrons drift from one end of the conductor to the other under the influence of the electric field.

The larger the cross-sectional area of the conductor, the more electrons are available to carry the current, so the lower the resistance. The longer the conductor, the more scattering events occur in each electron’s path through the material, so the higher the resistance. Different materials also affect the resistance.