Last Week's Question

Air breaks down forming an arc at field strengths of approximately,

  1. 25,000 volts
  2. 250,000 volts
  3. 30,000 volts/cm
  4. 300,000 volts/cm

Answer

ESD Discharge to a Laptop Computer The correct answer is "c". At high temperatures or in the presence of strong electric fields, air breaks down forming a plasma with enough free electrons to conduct electricity. The precise field strength required to break down air at room temperature depends on many factors, but it is on the order of 30,000 volts/cm. The first two choices in the question above can be eliminated, because "volts" is not a unit of field strength. An air discharge from an ESD simulator set to 30 kV will occur when the tip is approximately a centimeter from a grounded object.

Note: Air discharges over a plastic surface, or through seams in a plastic enclosure, can travel several times farther than open-air discharges.

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