Basic wall wart AC question

[sweesiong78]

Why is it when I stick just one probe of my multimeter into the pin of a plugged in  wall wart I can detect the 60Hz signal on my multimeter?  how is the multimeter able to complete the circuit?

[Psi]

The single connection provides a AC cycle reference between your meter and the mains making it easier for the meter to pickup 60Hz RF noise in the air around you. At least, that is how it was explained to me. Because it's AC, mains gets transmitted into the air.

[David Hess]

Capacitive coupling into the other multimeter lead generally from earth ground can provide enough signal into the 10 Mohm and roughly 200 picofarad input impedance of the multimeter.

This is not recommended but if you hold one lead in your hand, you can use the other to tell the difference between hot and neutral or ground.

[kolbep]

If you do hold the other probe in your hand, double check that your dmm is not on resistance or current ranges #Ouch#Lfmf

[German_EE]

I suspect that it is 50/60Hz fields. If I switch my bench DVM to 0,3VAC then I get a varying signal of about 0,15V with nothing attached and 0,26V with the leads plugged in but not connected at the other end.