EFFECT OF ELECTRIC CURRENT :        

(a)    Heating Effect of Electric current : 
        As you know, electric currents flow through a conductor. This flow experiences some resistance from the conductor. As a result some electricity changes into heat energy. Copper and aluminium offer very small amount of resistance. So, when electric              currents flow through them, they produce very small amount of heat. Tungsten and nichrome offer a large resistance. 
      When electric current pass through them, they produce a large amount of heat. Heating effect is used in electric iron, electric heater, electric toaster, electric kettle, electric oven, geyser, etc. When electric current is passed through the heating element of         these devices, heat is produced.


Example :
    (i) Electric Heater :

 

    (ii) Electric Iron :

 

The amount of heat produced in a wire depends on its material, length and thickness, Strength of the electric current. Thus, for different requirements, the wires of different requirements, the wires of different materials and different lengths and thicknesses are used.

The filament of an electric bulb gets heated to such a high temperature that it starts glowing.

Electric fuse :
    Fuse
    A fuse is a small piece of wire made of lead and tin It is a safety device which limits the current in an electric circuit and prevent short circuits. It is placed in the live wire at the entry point of the current. If the current in a circuit exceeds a specified value, the     fuse wire melts and breaks the electric circuit.

   The common type of fuse consists of a porcelain holder fitted with metallic terminals. The fuse wire is screwed between these terminals. The holder fits into a porcelain socket provided with a live wire. When the holder is in position, current will flow in the         circuit.

Characteristics of a Fuse
    • It has a short length wire with a low melting point. The fuse wire is made of an alloy containing equal amounts of lead and tin. It melts at about 200°C.
    • Fuse wire has higher resistance and its temperature rises much faster than the connecting copper wire in case of  overload.

(a) Fuse                                       (b) Fuse wire when connected                   (c) Broken fuse wire

Fuse wire in an electric circuit

Miniature circuit breaker (MCB)
A miniature circuit breaker (or MCB) is an alternative arrangement for fuse. The main problem with fuses is that whenever a fuse wire blows up, it needs immediate replacement. But in an MCB, we need not to face such a problem. It is placed in series in a given electric circuit. If the current exceeds the specified value, the MCB trips, i.e., puts off the switch and thus, the electric supply is cut off. It can be reset after correcting the fault.

 

Fuses of different rating are used for different purposes. It can be of 1 ampere, 2 ampere, 3 ampere and 5 ampere.

Short and Overload Circuit :
    Now imagine in a circuit, if a 2000 W room heater is used. It will draw a large amount of current. This in turn will heat the connecting copper wires to such an extent that plastic insulation on them will melt. Now the bare wires will come in contact with one       another. This will cause electric sparking and hence an electric fire. Such a circuit is called overloaded circuit and the sparking which causes fire is due to short circuit. 
  Overload in an electric circuit, therefore, is a condition when it draws more current than it is designed for. Short circuit occurs when a naked live wire and a neutral wire come in contact, by passing the electric device in the circuit which in turn, occurs due to    overload or the connection of the live wire with the earth wire.

  Short circuiting causes a greater loss of property and life every year in the homes and factories.
  Hence a fuse is the weakest part in an electric circuit, which melts and breaks the electric circuit when the circuit gets overloaded.

(i)    Due to a large current            
(ii)    Due to short circuiting
(iii)    Due to fluctuations of current in power supply system

So it may be prevented by proper uses of fuse.

(b)     Chemical Effect of Current (Electroplating) 
        When an electric current is passed through water containing sulphuric acid, the water breaks up into its components hydrogen and oxygen. Therefore an electric current can cause a chemical change. This effect of electric current is used in electroplating .       Electroplating :The method of plating one metal object with another metal by means of electricity is called electroplating. The metal which is to be electroplated is made cathode and the metal to be deposited is made  anode while the soluble salt of the           same metal serves as the electrolyte. When a current is passed, a thin film of metal is deposited on the metal, which becomes electroplated.
       Eg. : Let we are having a steel razor blade  is to be electroplated with copper.

3.    To show the heating effect of current on a bulb :
    • Insert a bulb between the cell and the conducting copper wire as shown in figure.
    • What do you observe after a few minutes? Does the end of the copper wire become warm again? No, why has the temperature not gone up? Now touch the bu'lb. Do you observe any heating effect?
    You will observe that the temperature at the ends of the copper wire remains unchanged but the glass of the bulb gets heated.
    The heating of the bulb in this activity shows the heating effect of current on the bulb.

 Introduction of bulb reduces the current in flow in the circuit 

 

4.    To show heating effect of current on nichrome :
       Take a 5 cm long nichrome wire, make a loop of it and connect it to a battery of two cells with the help of copper wires as shown in figure. Note your observations.

      You will observe that the loop of nichrome wire gets red hot.The electrical energy changes to heat energy and therefore the wire gets red hot.

Loop of nichrome becomes hot when current passes through it

 

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