Rajasthan Board RBSE Class 8 Science Notes Chapter 11 Effects of Electric Current
Today we use many electric appliances like iron, heater, oven, bulb, bell, toaster etc. Modern life I is incomplete without electricity. Some of the appliances get heated while electric current pass
through them but some like electric bell produce sound.
Heating effect of Electric Current:
Wind an nichrome wire on a pencil attach its one end with cell and other with electric circuit. As soon as the key is attached to plug, electric current starts flowing. After some time when we touch wire, it becomes hot. When close the circuit, wire becomes cool. Hence, when electric current is passed through a good conductor, it becomes heated, this is called heating effect of electric current. Electric oven, toaster, rod, iron, bulb are the appliances related to heating effect of electricity.
Fuse:
Electricity supply in our homes use three types of wires. Socket in homes have three holes. An electrician test the supply of electricity with an instrument called tester. The hole where tester is inserted and light glows, is called phase. Generally in domestic electric circuit red plastic coated wire is used. The phase in which light do not glow in the tester is called neutral end. On neutral wire the voltage is zero. Generally black plastic coated wire is used as neutral wire, between these two wires 220 volt electricity is received. The third wire is the earthing wire, with green plastic coated.
This wire is connected with a copper plate burned deep under the earth. It is a security measure which ensures that if phase is touching with the metallic part of any electric appliance, then the person who is using that appliance should not get severe electric shock.
Short Circuit:
When due to any reason phase and neutral joins directly, it is called short circuit. In such case very high voltage passes which causes fire due to high heating effect and could burn. Some times when more than one appliances are attached to single socket, it is called over loading on electric circuit. We should not attach more than one appliances or plugs in one socket.
Causes of Short Circuit:
- When quantity of current is more than limit of security, wire gets heated and plastic coat melts it allows phase and neutral to join and cause short circuit.
- When wires become old they break and cause short circuit.
Harms from Short Circuit:
Due to short circuit high voltage current flow which results into fire and can cause severe accidents. To overcome this and save electric appliances in the series of electric circuit such a plug should use which could melt when limit of security cross, it closes
the circuit such a wire is called fuse wire. Such a special wire is used today in expensive appliances like T.V., Fridge etc.
How does a fuse work?:
When quantity of electric current flows more than standard amount then it increases the temperature of fuse wire. It causes melting of fuse wire and breaks electric circuit. So, fuse wire is kept in metallic end porcelin or bad conductor cartage. Fuse wire is made-up of generally copper, zinc and tin i.e. mixed metal, whose melting point is lower than the wire used in the electric circuit of electric appliances. When electricity is supplied over then this wire breaks by melting.
In condition of over loading or short circuit and flow of electricity stops in circuit, hence we should always use ISI marked fuse. So fire accidents could be avoid. Now a days Miniature Circuit Breaker (M.C.B) are use in place of fuse. These are those switches which automatically close when excess current is supplied. When we re-start then circuit again started working.
Magnetic effect of Electric Current:
Take a magnet near a stable magnetic needles, it displaces. If a wire is set up on a card board and a compass or magnetic needle is kept near it, move the card board in such a way that needle of compass come just under the wire observation – Join the both ends of the wire with a cell.
It is observed that the wire kept near the magnetic needle gets flow of electricity and magnetic needle is deflected. By these observations a scientist name Aursted discovered the magnetic effect of electric current. When electric current flows through a good conductor then wire acts as a magnet. It is called magnetic effect of electric current. Electric bell, crane, telephone, telegraph etc. work on this effect. In all this appliances electric magnet is used.
Electromagnet:
Take 10-15 cm tong iron nail and a 50 cm long copper enamel coated wire remove enamel by rubbing its both ends with a sand paper join both ends with a cell and key and complete the circuit. Press the key and allow electric current to flow. If pin is brought near the nail it attracts it. The nail behaves like a magnet when electric current is flow through it. Such a magnet is called electric magnet.
Electric Bell:
It contains following elements:
- coil
- iron Plate
- contact screw
- hammer
- bell.
In coil of iron ore copper wires are join place the iron plate closely attached, with the hammer on the other it is attached to screw, when switch is on electric current flows and due to effect of it coil works as a magnet and attracts iron plate towards it, and due to strikes with it bell rings, when electric magnet attracts iron plate its contact with screw breaks and electric circuit also breaks, hence coil do not act as magnet if this process is repeated again and again.
Uses of Electromagnet:
- To separate things from scrap.
- Accidentally pieces of magnet fall in eyes are removed from eyes by an electric magnet.
- Electric magnetic crane is used to lift heavy iron goods.
- Bad conductor: Those solids which do not allow electricity to pass through them like rubber, plastic, wood etc. are called bad conductor of electricity.
Electricity Flow in Liquids:
Keep a magnetic needle in the tray of match box and wind it with a plastic coated copper wire. Connect its one end to battery and leave other free, if there ends are connected, needle shows deflection. In this ways two free ends wire tester is prepared. Now keep distilled water in a dry plastic lid in between two wires. It conducts electric flow. We see that good conductors of liquids are solution of acids, alkalies and salts, etc.
Chemical effect of Electric Current:
When electric current flows through any good conductor solution then it creates an effect in that solution; for example.
Take out two carbon rods from unused cells. Clean their caps with sand paper and wind copper wire on them and connect with battery. These two rods are called electrodes. Plate connected with positive (+ve) terminal is called anode and (-ve) terminal with which plate is attached is cafled cathode.
The two lines bigger represents (+ve) terminal and smaller (-ve) terminal. Dip these two terminals either in lemon juice or sodium chloride solution in a plastic container or in a glass. Take precaution that caps of both the terminals should be out of solution, wait for 3-4 minutes and observe the electrodes. We see that bubbles come out and plates are coated with ions. It happens due to chemical reactions took place. Due to flow of electricity in the solution colour of solution can be changed, but these reactions depend upon metal of electrodes and solutions. These are called chemical effect of electric current on chemicals.
Electroplating:
When electricity is passed through good conductor solution the solution divides or break down its elements (ions) which is used in electroplating. For example when electricity is passed in CuSO4 solution taken in a beaker in which two plates sized 10 cm x 4 cm are dipped and connect with battery. It breaks down into copper and sulphate ions. Copper is transferred to (-ve) plate. When any metal is coated by deposition through electricity then this process is called electroplating. It is used commercially in industries like: coating of gold or silver on metals, some parts of a car, taps of bathrooms, gas burner, handle of cycles, rim of wheels are coated with chromium. To protect irop from decay and rusting, iron is plated with zinc.