A CAR BATTERY

A battery consists of numbers of cells.Six-volt batteries have three cells.Twelve-volt batteries have six cells.The cells have positive and negative plates.Most plates are made of lead.They are usually named electrodes.Positive electrodes are termed anodes,and negative electrodes ar known as cathodes.Both anodes and cathodes are immersed in a liquid.This liquid is called an electrolyte.The electrolyte generally contain an acid.For example,a common electrolyte consists of sulphuric acid(H2SO4)plus water.The battery works with produces electricity because the acid reacts with the electrodes.Electrick current flows from the negative electrode(cathode)to the positive electrode(anode)through the electrolyte.When the reaction between the sulphuric acid and the lead finishes,the electrolyte is very weak.The battery is flat and therefore cannot produce any electricity.When the battery is recharged with an electric current,the electrodes are converted back to their original condition.On most cars the earth is connected to the negative terminal,on some to the positif terminal.Check carefully before removing the leads.

KIND OF STEELS

Steel is an alloy of iron with carbon and we can improve its properti by adding other elements such as tungsten.Alloy steels are very strong and tough.They are probably the most important metals for knives,tools,and machinery. There are many types of steels such as low carbon steel,mild steel,medium carbon steel,and high carbon steel.Low carbon steel is not very hard.Its the softest of the steels.Mild steel is harder than low carbon steel.Medium carbon steel is even harder.The high carbon steel is the hardest. Low carbon steel is not very strong.It is the weakest of the steels.Mild steel is stronger than low carbon steel.Medium carbon steel is even stronger.The high carbon steel is the strongest. Furthermore,we can also classify high carbon steels into three kinds,spring,steel,and tool steel.Hardsteel is as hard as spring steel.The tool steel is the hardest and it is often used for cutting tools such as chisels and drills. High carbon steel has a great strength and hardness.It is easy for us identify high carbon steel in the spark test;namely,when we grind it,high carbon steel always produces showers of sparks.

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