Theory:

Testing the heating effect of current:
A simple electric circuit is made using iron nails, thermocol, nichrome wire, a cell, and a switch.
 
Two nails are placed on a thermocol and are connected with a cell and a switch. A nichrome wire of \(10\ cm\) long is tied between the nails. The nichrome wire can be seen in an electric heater and electric repair shops.
 
When the switch is in the 'OFF' state, no current flows through the circuit. So, when the wire is touched at this time, nothing is felt. But when the switch is turned 'ON', the electric current flows through the circuit making the wire hot. This is called as the heating effect of the electric current.
 
Important!
If the switch is kept in the 'ON' position for a long time, the cell may become weak and gets worn out quickly. So, never keep the switch in the 'ON' state for a long time if it is not in use.
Heating effect in appliances:
Many electrical appliances use this heating effect to make our work easier.
Example:
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Electric room heater
 
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Geyser
 
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Electric cooker
In all these appliances, a coil of wire called an element is present. When these appliances are switched on, electric current flows through the circuit. This makes the element in the appliances to give out heat.
 
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Element in the appliance
  
Properties of the element:
The amount of heating the element depends on the material, length and thickness of the coil. These properties can vary depending on the requirements of heat.
Compact Fluorescent Lamps:
Incandescent electric bulbs produce light as well as heat. When electricity is passed through the bulb, some amount of it is wasted in the form of heat. Compact Fluorescent Lamps (CFLs) and the fluorescent tube-lights are better than the incandescent electric bulbs. They are more efficient in producing electricity. Compact Fluorescent Lamps (CFLs) and the fluorescent tube-lights contains a toxic mercury vapour. It should be disposed off properly if they get damaged.
 
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Compact Fluorescent Lamp
Light Emitting Diode:
Light Emitting Diode (LED) bulbs are more efficient than any other bulbs. They consume less amount of electricity than CFLs, incandescent bulbs, and fluorescent tubes. Hence, LEDs are preferred more. It is good to use electrical appliances that are electricity efficient.
  
ISI mark:
Bureau of Indian Standards in New Delhi gives an assurance of conformity to the specifications given on the products called Indian Standards Institution (ISI) mark. It is a Standard Mark on products. It is always suggested to use products having ISI mark.
 
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Reference:
Bureau of Indian Standards for ISI mark