Question

A current flowing through you of more than 5 ma is considered dangerous. Why do we see warnings about high voltage, rather than high current? What voltages are dangerous even if the skin is dry? (Dry skin has a resistance of 100 kohms while wet skin can be much less.) An electroencephalogram (EEG) is a recording of differences in voltage observed on the scalp by attaching electrical contacts. If voltage differences that are observed are about 0.5 mv, and the resistance of the skin is about 10 kohms, what size currents are involved?

Answer 1

V = 500 volts

I = 50 nA

Step-by-step explanation:

We usually see 'high voltage' sign rather than 'high current' this is due to the fact that the amount of current depends upon the resistance of the body,

The relation of voltage, current and resistance is given by Ohm's law,

V = IR

I = V/R

As you can see, current and resistance are inversely related, the lower the resistance of the body, the higher will be the current flowing through the body.

What voltages are dangerous even if the skin is dry?

A dry human body has a resistance of approximately 100 kΩ and it gets reduced if the body is wet.

For a current of 5 mA, the corresponding voltage is,

V = 0.005*100,000

V = 500 volts

Therefore, for a dry human body, a voltage of 500 volts would be dangerous.

If voltage differences that are observed are about 0.5 mV, and the resistance of the skin is about 10 kΩ, what size currents are involved?

I = V/R

I = 0.0005/10,000

I = 50×10⁻⁹ A

I = 50 nA

Therefore, a current of 50 nA would be flowing through the EEG.