HEATING EFFECT OF ELECTRIC CURRENT

 An electric lamp will glow due to heating of the wire (filament) inside the air tightened glass tube

The filament heated up by the flow current through it.

The heat produced by filament reacts with inert gases inside the glass tube and emits the light

the following are some of the appliances used for heating purpose by utilising electric current

1) room heater

2) cooking food

3) electric iron

4) geysers

5) hair dryer

6) electric oven

7) electric kettle 

Activity-1:

1) connect a bulb with two insulated copper wires to the battery terminals

2) the bulb lights up

3) the bulb emits the light and also gives heat

Activity-2:

1) Connect the two ends of the  non insulated copper wires to battery terminals with out a bulb .

2)  The wire will get heated. Just touch and feel it hot

Good conductors:-

Copper , aluminium, iron.

Copper is a good conductor and electric current is conducted through it offers no resistance without producing heating effect

Bad conductors:-

Alloy of Nickel and chromium  called nichrome , tungsten 

Nichrome offers more resistance so produces more heat

Nichrome wires used in room and kitchen Heaters

A filament is a very thin wire made up of tungsten metal offers greater resistance produces more heat.

Some time material used as filament may melt due to High current flowing through it.

Amount of heat produced in appliances depends on:

a) the material of which the wire is made

b) the  length and thickness of the wire being used

C) the amount of electric current passing through it

ELECTRIC HEATER:-

we can use electric heater in the kitchen as well as in laboratory

The heat producing part in the heater is kaolin or asbestos

The heating element is like a spring made up of nichrome wire is passed through groves in the frame

Two ends of nichrome wire are fixed to kaolin frame and ended with connecting wire and plug

When this plug connected to electrical supply electric current passes through the nichrome wire which offers high resistance

Because of high resistance wire gets heated becomes red hot and radiates heat 

To avoid the short circuit  , the ends of the nichrome heating element are carefully sealed

ELECTRIC HOT -PLATE

Some changes are made in the manufacture of  electric heater.

Over a heating element of electric heater a thick iron plate is fixed

Iron plate absorbs  heat from nichrome wire and becomes hot

No need to use asbestos wire - mesh 

ELECTRIC FUSES AND MINIATURE CIRCUIT BREAKER:

FUSE:-

It is the protective device in an electric , which melts and breaks an electric circuit due to following reasons

1) when circuit overloaded due to large withdrawal of current

2) due to short circuit

3) due to fluctuations of current

MINIATURE CIRCUIT BREAKER:- 

When fuse melts due to High currents in electric circuit it is needed to replace the fuse , that the fuses cannot be reused  this problem is overcome by miniature circuit breaker  placed in series