Why when we touch osciloscope probe it shows 50Hz noise?

[op27]

Hello, I have asked this question from different people but never got a
satisfactory answer.
I want to know in terms of electromagnetic physics how 50 Hz frequency of
main is induced in our body and converted to voltage at oscilloscope probe.
Please answer only if you deeply understand this phenomenon. dose it depend
on current? i.e. if we get more currents from main it induces more noise?
how it depends to voltage?

thanks,

 

[Jasen Betts]

Hello, I have asked this question from different people but never got a
satisfactory answer.
I want to know in terms of electromagnetic physics how 50 Hz frequency of
main is induced in our body and converted to voltage at oscilloscope probe.
Please answer only if you deeply understand this phenomenon. dose it depend
on current? i.e. if we get more currents from main it induces more noise?
how it depends to voltage?

It depends on the degree to which your body is capacitatively coupled
to the mains. (and the degree to which it is earthed, and to a lesser
extent the magnetic flux and the area of the loop formed by the circuit
formed by touchiong the probe.

try touching the probe to a large piece of aluminium foil.

 

[op27]

It depends on the degree to which your body is capacitatively coupled
to the mains. (and the degree to which it is earthed, and to a lesser
extent the magnetic flux and the area of the loop formed by the circuit
formed by touchiong the probe.

try touching the probe to a large piece of aluminium foil.

So magnetic field that is produced when we draw current from mains can be
converted back to electrical current in our body and produces voltage. for
example when large currents are drawn e.g. welding it causes to some tiny
currents produced in our body?

the capacitance of our body should directly depends on our distance to
wirings inside the wall, isn't that?
why oscilloscope amplitude is about a few volts rather than 220V?
this peak to peak voltage depends on what ? can we calculate it?

 

[Sjouke Burry]

Hello, I have asked this question from different people but never got a
satisfactory answer.
I want to know in terms of electromagnetic physics how 50 Hz frequency of
main is induced in our body and converted to voltage at oscilloscope probe.
Please answer only if you deeply understand this phenomenon. dose it depend
on current? i.e. if we get more currents from main it induces more noise?
how it depends to voltage?

thanks,

You need to pack your head with aluminium foil.

 

[op27]

You need to pack your head with aluminium foil.

I said only reply if you understand the phenomenon. surely I don't need
advice from people who don't have anything in their head.

 

[op27]

I think my main mistake was that I was assuming a magnetic field rather than
electrical field produces this phenomenon. regards,

 

[Eeyore]

op27 wrote:

Because there's a lot of it about !

60 Hz in the USA etc.

Graham

 

[Eeyore]

I said only reply if you understand the phenomenon. surely I don't need
advice from people who don't have anything in their head.

http://en.wikipedia.org/wiki/Tin_foil_hat

Graham

 

[Rich Grise]

Quick diode tester:

Grab scope probe tip with your left hand. Observe 50/60 Hz cruddy sine
wave on scope.

Grab one end of diode with right hand, and touch free end to scope
ground.

I did this with a transistor once - I think it might have been a
darlington - but I did see gain.

Cheers!
Rich