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If a high
amount of charge builds up on
it can escape across a small distance
through air to a neutral or oppositely charged object.
You may have noticed that pulling
off a jumper or
other clothing over your head can cause crackling.
If the clothing is made from a synthetic fibre
(a plastic material which is a good insulator)
then charge is transferred as it rubs against
your hair (which is also a good insulator).
The crackling is the sound made by the charge jumping
through the air between the clothing and your hair.
How can a Car Door or a Radiator give you a Shock?
Touching a car door or a radiator can sometimes give
you a shock. If both the car seat and your clothing are
made from a synthetic fibre, then one rubs against the
other transferring charge as you step out of the car.
The charge then jumps the small air gap between your
finger and the car as you go to close the car door.
Similarly, if both a carpet and your
shoes are made from
synthetic materials, then charge is transferred as you walk
around. Touching a radiator will cause the charge to jump
the small air gap between your finger and the radiator.
The sensation of the charge on your skin feels unpleasant.
If your clothing, carpet,
shoes etc. are made from natural
fibres then you are much less likely to get a shock.
Natural fibres such as wool and cotton attract a small amount
of moisture (water) to their surface and this moisture allows
the material to conduct a little so the charge escapes before
it can build up enough to jump through air. If the air itself
is moist, the charge will also escape and no shock will occur.
How can Electrostatic Charge cause a Spark?
In the examples above, when charge jumps across a
air gap it causes a spark which can be dangerous.
Lightning is a natural example of a huge charge jumping
across a very large air gap between the ground and
the sky, and we know how dangerous lightning can be.
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