Electric Sparks

1. Feb 25, 2010

WilliamVeregg

I'm totally stuck on a physics problem. I've been looking through my notes and my book for the past hour and cannot find anything.

The question is

Find the distance at which an electric spark would arise between your hand and the metal doorknob if your hand carries a total charge of Q=50nanoC

Is there an equation to solve this? I've tried googling this also.

2. Feb 25, 2010

Stonebridge

This has to be open ended and you need to make a number of assumptions.
The dielectric strength of air is approximately 3 kV/mm. In other words, a pd of 3kV will produce a 1mm spark.
You need to estimate the pd between your body (hand) and the door knob. (Take the door to be zero)
Can you find an estimate for the capacitance of the human body?
If so, one estimate would involve using this and the charge given to find V.
However, the shape of the electrode (your hand) also plays an important role.