# Electronic – How does the tester screwdriver work

circuit analysisdielectricelectromagnetism

How does the tester screwdriver work? If I put the tester screwdriver inside the "hot wire" of an electrical socket, it lits up if I press my finger against the metal cap on top of the screwdriver. This happens also if I stand on a surface of isolating material, such as wood. I read elsewhere that this happens due to stray capacitance formed by the "hot wire", the human body, and the ground. One has

$$Z = R + \dfrac{1}{j \omega C}$$

for the impedance, so if C is high enough, the impedance should be close to r , the "effective resistance" of the formed circuit. Here I get lost; why r is small enough to cause a current in the range of mA even if I stand on an isolating surface?

So really what I am asking is how one may represent the system hot wire – screwdriver – human body – wooden floor – building – ground as an electrical circuit, and which parts of the physical system contribute to the resistance, capacitance (and inductance?) and in which proportion, even very approximately.