CLASS 8 CHEMICAL EFFECTS OF ELECTRIC CURRENT Effects of Electric Current 1. Heating Effect 2. Magnetic effect 3. Chemical Effect Working of an Electric Bulb: Due to the heating effect of current, the filament of the bulb gets heated to a high temperature and it starts glowing. ACTIVITY : TESTING CONDUCTION OF ELECTRICITY THROUGH LEMON JUICE using Simple circuit. Procedure Observation Result Bulb does not glow The current through a circuit is too weak, the filament does not get heated sufficiently and it does not glow. Arrange a conduction tester as shown. Lemon juice does not conduct electricity as easily as a metal. As a result, the circuit of the tester may be complete and yet the current through it may be too weak to make the bulb glow Magnestic Compass is a device to test the presence of magnetic property around current carrying wire. ACTIVITY : TESTING CONDUCTION OF ELECTRICITY THROUGH LEMON JUICE using Simple circuit and magnetic compass Procedure Observation Result Magnetic Compass needle deflects Deflection of magnetic compass indicates that the circuit is complete, and electricity passes through Lemon juice.
Arrange the conduction tester as shown by keeping a magnetic compass near the wire. Pass electricity Examples of Liquids that conducts Electricity. Solutions of acids Solutions of Bases Solutions of salts LED ( Light Emitting Diodes) (FA-2 5 MARKS) LED has no filament. There are two wires (called leads) attached to an LED. One lead is slightly longer than the other. The longer lead is always connected to the positive terminal of the battery and the shorter lead is connected to the negative terminal of the battery. Advantage of using LED lamps: Scientists who gor Nobel Prize for their work on LED ELECTROLYSIS When current is passed through a conducting liquid, it splits into its components. This process is called Electrolysis. Electrolyte The liquid through which electricity is passed during electrolysis is called electrolyte. Electrodes The rods used to pass electricity through an electrolyte are called electrodes. Types of Electrode Positive electrodes and Negative Electrodes.
Electrolysis of Water Discovered by William Nicholson Procedure Observation Result Observation When current is 1. bubbles of oxygen and passed water hydrogen are produced. splits into 2. Oxygen bubbles formed on hydrogen and the electrode connected to the oxygen. This is positive terminal of the battery 3. hydrogen bubbles formed called on the other electrode. Electrolysis of 4 More hydrogen is formed than water oxygen Electrodes Positive electrode Graphite rod (Anode) Negative Electrode Graphite rod(cathode) Electrolyte Water ( add one or two drops of dilute sulphuric acid to make it good conductor) Pass Electricity ELECTROPLATING The process of depositing a layer of any desired metal on another material, by means of electricity, is called electroplating. Eg; Chromium plating Silver plating Gold plating Galvanisation
Uses/ Advantages of Electro plating Chromium Plating Chromium has a shiny appearance. It does not corrode. It resists scratches. Chromium is expensive.so the object is made from a cheaper metal like iron and only a coating of chromium over it is deposited. Gold Plating/ Silver plating Jewellery makers electroplate silver and gold on less expensive metals. These ornaments have the appearance of silver or gold but are much less expensive. Tin Plating Tin cans, used for storing food, are made by electroplating tin onto iron. Tin is less reactive than iron. Thus, food does not come into contact with iron and is protected from getting spoilt. Zinc Plating / Galvanization Iron has good strength. But iron tends to corrode and rust. So, a coating of zinc is deposited on iron to protect it from corrosion and formation of rust. Disavantage of electro plating In the electroplating factories the disposal of the used conducting solution is a major problem. It is a polluting waste and there are specific disposal guidelines to protect the environment.