It has to do with the safety laws. The third wire in the wall socket is connected to the earth at the building wall where the mains power comes in.
If the plug has two pins, the device is required to have two independent layers of insulation around the outer surface. If the outer surface is metal, it is connected to the third pin.
ahan,
can ne one tell me wats the difference between earthing and grounding,
i personally think that the third pin is for grounding,
but now this question has intrigued me a bit to ask u for a diff between earthing and grounding
ahan,
can ne one tell me wats the difference between earthing and grounding,
i personally think that the third pin is for grounding,
but now this question has intrigued me a bit to ask u for a diff between earthing and grounding