| | Alternating current
| Direct current
|
| Direction of flow of charges
| | |
| Supply of current
(What generates the current?)
| | |
| Amount of energy that can be carried
| | |
| Conversion (What device is used to convert this type of current to another?)
| | |
| Use and application
| | |
| Diagram
| | |
Exercise 26. Underline the correct word(s) from the brackets to complete the sentences about inverters and different stages of AC generation and supply.
1. Inverters convert (direct current/ alternation current) to (direct current/ alternation current).
2. If an inverter is used to supply electric appliances in a home, it must copy the supply ofmains electricity produced by (batteries/ generators) at power stations.
3. Most inverters can produce a current which (flows/ alternates) precisely at the required (frequency/ voltage), for example, 50 (hertz/ volts) (50 cycles per second).
4. After the step-up transformer, the current enters a (distribution/ transmission) line.
5. The current goes from the last step-down transformer to a (distribution/ transmission) line.
6. The current leaves the power (grid/ station) and enters the home.
7. Amperage is reduced and voltage is increased by a (step-up/ step-down) transformer.
Exercise 27. It is convenient to classify materials in terms of the ability of electrons to move through the material. Match the materials with their description and with appropriate examples.
| Materials
| Description
| Examples
|
| Electrical conductors
| A third class of materials, and their electrical properties are somewhere between those of insulators and those of conductors. The electrical properties of of these materials can be changed over many orders of magnitude by the addition of controlled amounts of certain atoms to the materials.
| Glass,
rubber,
wood
|
| Electrical insulators
| Materials in which some of the electrons are free electrons that are not bound to atoms and can move relatively freely through the material. When such materials are charged in some small region, the charge readily distributes itself over the entire material surface of the material.
| Silicon andger-manium (used in electronic chips)
|
| Semiconductors
| Materials in which all electrons are bound to atoms and cannot move freely through the material. When such materials are charged by rubbing, only the area rubbed becomes charged, and the charged particles are unable to move to other regions of the material.
| Copper, aluminum, silver
|
