Friday, February 27, 2009

Static Electricity - 2


Pressure-induced charge separation
Applied mechanical stress generates a separation of charge in certain types of crystals and ceramics molecules.

Heat-induced charge separation
Heating generates a separation of charge in the atoms or molecules of certain materials. All pyroelectric materials are also piezoelectric. The atomic or molecular properties of heat and pressure response are closely related.

Charge-induced charge separation
A charged object brought into the vicinity of an electrically neutral object will cause a separation of charge within the conductor. Charges of the same polarity are repelled and charges of the opposite polarity are attracted. As the force due to the interaction of electric charges falls off rapidly with increasing distance, the effect of the closer (opposite polarity) charges is greater and the two objects feel a force of attraction. The effect is most pronounced when the neutral object is an electrical conductor as the charges are more free to move around. Careful grounding of part of an object with a charge-induced charge separation can permanently add or remove electrons, leaving the object with a global, permanent charge. This process is integral to the workings of the Van de Graaf Generator, a device commonly used to demonstrate the effects of static electricity.

Static discharge
The spark associated with static electricity is caused by electrostatic discharge, or simply static discharge, as excess charge is neutralized by a flow of charges from or to the surroundings. The feeling of a static electric shock is caused by the stimulation of nerves as the neutralizing current flows through the human body. Due to the ubiquitous presence of water in places inhabited by people, the accumulated charge is generally not enough to cause a dangerously high current.

Despite the apparently innocuous nature of static electricity as we generally experience it, there can be significant risks associated with it in circumstances where large charges may accumulate in the presence of sensitive materials or devices.


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