Suppose that after walking across a carpeted floor you reach for a doorknob and just before you touch it a spark jumps 0.95cm from your finger to the knob. Find the minimum voltage needed between your finger and the doorknob to generate this spark. The minimum field that can produce a spark in air is 3.0x10^6 V/m. V = V

To solve this problem we will consider the definition of Minimum Energy, as the change between the minimum voltage and its distance. Mathematically it can be written as

Rearranging to find the Voltage,

Replacing,

Therefore the minimum voltage needed between your finger and the doorknob to generate this spark is 28.5kV

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the minimum amperage that the current in this wire would have to have so that its weight is completely supported by the magnetic force due to earth's field, assuming that no other forces except gravity act on it