Around the sun leaving a bright trail behind. For more than
Even though they are taking over some of the tasks that were once accomplished by our own brains, computers are not replacing us - at least not yet
Yüklə 2,03 Mb.
|
- Bu səhifədəki naviqasiya:
- In addition
- . Therefore
- In fact
- . However
Even though they are taking over some of the tasks that were once accomplished by our own brains, computers are not replacing us - at least not yet . Our brain has more than 10 billion cells. A computer has only a few hundred thousand parts. For some time to come, then, we can safely say that our brains are at least 10,000 times more complex than a computer. How we use them is for us, not the computer, to decide.
70 ELECTRON THEOR At one time, students used to be told: t9We don't know what electricity is, we don't know how electricity goes through a solid wire," etc. The electron theory explains these things clearly and simply. In addition, it explains the true meaning of voltage, resistance, etc. Therefore, an understanding of the electron theory is basic to the understanding of the electrical and electronic theory. Scientists now agree that our universe is basically dependent on two factors, one of which is matter, the other, energy. Matter is anything that occupies space and has weight. It can exist in any of the three forms: solid, liquid or gas. Matter is composed of protons, neutrons and electrons. The proton has a positive charge. This component has very little weight The neutron has no charge, but it supplies almost all the weight of matter. The electron has a negative charge. It also has very little weight. If we could look at the structure of a piece of copper, we would find that it consists of a specific number of protons, neutrons, and electrons arranged in some particular way. In a piece of iron, a certain number of protons, neutrons, and electrons are arranged in a different way. The proton of iron is identical to that of copper and other elementt They are all made up of the same components. It is the arrangement of these components that makes them different. The electrons of an atom are arranged in shells around the nucleus. The electrons in the last shell are called 'valence' electrons and the electrical properties of a material are dependent on the number of SnQh electrons. Atoms with less than four valence electrons give up one or more electrons, and the fewer the valence electrons, the easier this becomes. Atoms with more than 4 electrons in their last shell take one or more additional electrons. The conduction of electricity is made possible by the free electrons in the outer shell. Metals are good conductors of electricity as they have less than 4 valence electrons. These electrons aren't strongly attached to the nucleus, but the ones in the inner shell are. Therefore, in a metal, they can move easily from one nucleus to another.
153 HYDROPONICS Hydroponics is the technique of growing plants in water. It is generally thought that plants need soil for growing. In fact, what they need is the nutrients (vitamins and minerals) and moisture contained in the soil and these can be supplied through water, as well as through soil. Hydroponics is not a new process. As long ago as the 1690's, an English physician tried growing plants in water in a laboratory experiment. However, it was not Until the 1800's that German researchers used this method to develop many of the formulas for plant nutrient solutions still in use today. About a generation ago, hydroponics moved out of the research laboratory into practical use. In the past 40 years, hydroponic farming has progressed in a number of areas, especially in those where water is in short supply and temperatures are too extreme for ordinary agriculture. This is because hydroponic farming is the only economical solution in such desert areas. Yüklə 2,03 Mb. Dostları ilə paylaş:
|