Where There Is Charge, There Can Be Sparks!

[usa2be4me]

In this experiment, in the determining voltage paragraph, the example given is at 1 atm. What is the general pressure in a classroom?
How will I know exactly what the voltage is in my experiment?
Thank you for your help!

[raytrent]

Probably for this experiment the difference between your classroom pressure and 1 atmosphere won't be signficant. However, if you're worried about it, you could measure it with a barometer. Depending on the units of your barometer, 1 atmosphere might be several different numbers -- you can find more information here: http://en.wikipedia.org/wiki/Atmospheric_pressure

[rmarz]

You haven't described your experiment in detail, but to try to answer your specific question - the 'general pressure' in your classroom will be 1 atmosphere. You can research that value from many sources, but it is close to 14.5 PSI, or 30 " of mercury or 100 kPa. The effects of temperature and pressure can alter the dielectric value of air to inhibit an electrical arc. When you ask 'how do I know the voltage?' you are probably referring to this dielectric value, around 3,000 volts per millimeter of air gap. Therefore if you increase voltage across a 1 mm gap, you can assume that the voltage will be about 3,000 volts when you first observe the arc. In that the this is a 'field strength' you can reduce or broaden the physical gap to observe lower or higher voltages, but the 3,000 volts/mm is constant.

Rick Marz