Answer the following questions

1. What types of heat transmission do you know?

2. What do you call conduction?

3. What is convection?

4. What good conductors of heat do you know?

5. What is radiation?

Sources of energy

We use many different energy sources to do work for us. Energy sources are classified into two groups — renewable and nonrenewable. Renewable and nonrenewable energy can be converted into secondary energy sources like electricity and hydrogen.

In some countries most of our energy comes from nonrenewable energy sources. Coal, petroleum, natural gas, propane, and uranium are nonrenewable energy sources. They are used to make electricity, to heat our homes, to move our cars, and to manufacture all kinds of products.

These energy sources are called nonrenewable because their supplies are limited. Petroleum, for example, was formed millions of years ago. We can’t make more petroleum in a short time.

Renewable energy sources include biomass, geothermal energy, hydropower, solar energy, and wind energy. They are called renewable energy sources because they are replenished in a short time. Day after day, the sun shines, the wind blows, and the rivers flow. We use renewable energy sources mainly to make electricity.

(870)

Answer the following questions

1. What are renewable energy sources?

2. What are nonrenewable energy sources?

3. What is the difference between them?

Electric energy

Electric power is generated by converting heat, light, chemical energy, or mechanical energy to electrical energy. Most electrical energy is produced in large power stations by the conversion of mechanical energy or heat. The mechanical energy of falling water is used to drive turbine generators in hydroelectric stations. The heat derived by burning coal, oil, or other fossil fuels is used to operate steam turbines or internal-combustion engines that drive electric generators. Also the heat from fissioning of uranium or plutonium is used to generate steam for the turbine generator in a nuclear power plant.

Electricity is clean, inexpensive, and easily transmitted over long distances. It is used to operate lights, pumps, elevators, power tools, furnaces, refrigerators, air-conditioners, radios, television-sets, industrial machinery, and many other kinds of equipment. It has been counted that in developed countries about 43% of the electric power is generally used for industrial purposes, 32% in homes, and 21% in commercial enterprises.

(900)

Дата добавления: 2015-08-09