On a dry winter day, if you scuff your feet across a carpet, you build up a char

Question

On a dry winter day, if you scuff your feet
across a carpet, you build up a charge and get
a shock when you touch a metal doorknob.
In a dark room you can actually see a spark
about 2 cm long. Air breaks down at a field
strength of 3 × 10^6 N/C.
How much charge have you built up? As-
sume that just before the spark occurs, all the
charge is in your finger, drawn there by in-
duction due to the proximity of the doorknob.
Approximate your fingertip as a sphere of di-
ameter 1.42 cm, and assume that there is an
equal amount of charge on the doorknob 2 cm
away.
Answer in units of C

How many electrons does this correspond to?
The elemental charge is 1.60218 × 10-19 C.

Explanation / Answer

Kq/r^2+Kq/r^2=3 × 10^6 N/C.[r=2+1.42 =3.42cm] q=1.9494*10^-9 c no of e=1.2184*10^10

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