Reading

Date: 2015-10-07; view: 424.

7. Read the text, highlight key words and title each paragraph:

1.________________________________

Electricity is a form of energy, evident from the fact that it runs machinery and can be transformed into other types of energy such as light and heat. Electricity is created when a state of unbalanced charges exists.

2.________________________________

Electrical charges accumulated at one point are called static electricity. Static electricity is electricity at rest. It is produced by friction or rubbing that can make atoms of some substances lose electrons and become positively charged. Other substances gain electrons easily and become negatively charged. The release of static electricity when two objects come into contact is called electrostatic discharge (ESD). This is a sudden flow of electricity between two electrically charged objects caused by contact.

3.______________________________

Electricity that moves from one place to another is called current electricity. Current is a stream of moving electrons. This is the type of electricity that does the most work for a man. It makes motors spin, lights light up and heaters warm the premises. Unlike static electricity, current electricity must flow through a conductor. Electricity can flow through any material. How easily it flows is called resistance. Different materials have different level of resistance.

4.______________________________

Conductors are materials through which electricity can flow easily. They are materials with low resistance. A common conductor is copper. Copper wires conduct electricity. Opposite to conductors are insulators. These are the materials with high level of resistance. They prevent or block the flow of an electric charge and keep electricity from getting to unwanted areas. The plastic insulation around a copper wire is an example of an insulator. The resistance is measured in Ohms.

5.______________________________

There are two forms in which electricity can be generated: Direct Current (DC) and Alternating current (AC). DC is the type of electricity supplied by a battery. One terminal is positively charged, the other one is negatively charged, and electricity flows from one to the other, always in the same direction. AC also has a positive and a negative terminal, but the polarity and the direction of flow alternates many times per second. AC can travel well over long distances.