8 Science Chapter 14 Chemical Effects Of Electric Current

Chapter Notes and Summary
• material which allow electric current to pass through them easily are called good conductors of electricity.
The materials which do not allow electric current to pass through them are called poor conductors of electricity.
• Some liquids are good conductors of electricity and some are poor conductors of electricity.
• Due to heating effect of current, filament of bulb gets heated and starts glowing. If current is weak, filament does not get heated and it does not glow.
• LED (Light Emitting Diodes) can be used in place of electric bulb in tester. LED glows even if a weak electric current flows through it.
• Distilled water is a poor conductor of electricity. Impure water or salt dissolved water can conduct electricity.
• passage of an electric current through a conducting solution causes chemical reaction. As a result bubbles of gas may be formed on electrodes. Deposits can also be seen on electrodes.
• Electroplating is widely used in industries for coating one metal object with another metals.
• electrode connected to positive terminal of battery is called anode and one connected to negative terminal of battery is called cathode.
Uses of Electroplating : Electroplating is widely used in industry for coating metal objects within a thin layer of a different metal. This may be done to :
• make objects appear shiny, l make objects resistant to scratches l coat less reactive metal on more reactive metals to protect from getting spoil.
• electroplate less expensive metals with silver and gold to make ornaments.
For example :
• Chromium has a shiny appearance, doesn’t corrode and is resistant to scratches. But, chromium is expensive and it is not economical to make whole object out of chromium. So, objects, such as taps, car parts, wheel rims,
etc. are made from a cheaper metal and electroplated with chromium.
• Jewellery made of cheap metals is electroplated with silver or gold to appear as if made of silver or gold.
• Tin is less reactive than iron. So, iron cans used for food items are electroplated with tin to prevent spoilage from contact with iron.
• Iron used in bridges and automobiles is electroplated with a coating of zinc to protect it from corrosion and formation of rust.
• disposal of used conducting solution of electroplating factories is a major problem. It is a polluting waste and there are specific disposal guidelines to protect environment.
• There are three effects of electricity :
Chemical effect (ii) Heating effect (iii) Magnetic effect
(i) Chemical Effect :
When electric current is passed through conducting liquids, then chemical changes take place.
This is called chemical effect of electric current.
(ii) Heating Effect :
current flowing in circuit is usually detected by using a small electric bulb like torch bulb. When an electric current flows through a bulb, then due to heating effect of current filament of bulb gets heated to a high temperature and it starts glowing, this phenomenon is known as heating effect of electric current.
(iii) Magnetic Effect :
current flowing in a wire can be defected by deflection of magnetic needle kept near by a current flowing wire. This is called magnetic effect of current.

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