# Relation between voltage and current [duplicate]

What I know is that voltage is the electrical pressure which is required to drive the electrons in a circuit. According to that we have higher currents when there is a high voltage. Ohm's law confirms that. What I don't understand is that some books say that it is the current that is more dangerous to the human body and not the voltage. What I mean is higher currents are dangerous but high voltages aren't. But if we have a high voltage aren't we indirectly meaning that there is high current since they are directly proportional to each other.

## marked as duplicate by Brandon Enright, Abhimanyu Pallavi Sudhir, akhmeteli, Qmechanic♦Dec 11 '13 at 12:55

The current you are going to get through your body depends on the voltage and on the resistance.

You can touch a 110 V exposed cable using a piece of metal or a piece of plastic - in both cases the voltage is the same, but the resulting current - and hence the danger - is greater in the first (metal) case.

• Thanks. I wanted to ask one more thing. If we have an alternating current and if its frequency is sixty hertz. Then how is it more dangerous than the alternating current at a frequency of ten hertz. I couldn't understand this – Rahul Chitta Dec 10 '13 at 18:44

I always thought this rule of thumb was a bit silly - current kills because it was driven by a voltage, otherwise there would have been no current.

The rule arises because of the variability of skin resistance. Little voltage applied internally across your heart will kill you, but the skin's variability means that it is impossible to say what external voltage will cause this voltage.

If we specify the current, however, the problem is sidestepped. A lethal current requires whatever external voltage is needed to drive it.

• Thanks. I wanted to ask one more thing. If we have an alternating current and if its frequency is sixty hertz. Then how is it more dangerous than the alternating current at a frequency of ten hertz. I couldn't understand this. – Rahul Chitta Dec 10 '13 at 18:21
• This is no longer a physics questions, but a biological one. However consider that your muscles probably wouldn't appreciate being yanked in opposite directions at 60 times a second or 10. But the physiological response vs. frequency is not something I can answer. – Lenzuola Dec 11 '13 at 6:37

What kills you is the current not the voltage, as you read on your books.

Of course that you to have a voltage difference so the current can flow, but it does not determine how strong the current will be. I do not know if I would die if I touch something with 1 kV. That's because the current will depend on the sum of the resistance between me and the ground (it will depend if have rubber boots, or gloves, or if I am in the middle of a jump).

What I do know is: no matter the voltage I touched, I will die if 10 Amps pass through me (please do not consider miracles for the sake of the explanation)

• If there is a resistance then there will be a voltage drop. So are you saying that because of this voltage drop the magnitude of current goes down? – Rahul Chitta Dec 10 '13 at 19:01
• The presence of resistance doesn't change the voltage difference across the two places you're touching. Increasing the resistance simply decreases the resulting current flow. – xish Dec 10 '13 at 19:27
• @RahulChitta the external voltage applied is the sum of the voltage drop along the path of the current. In particular your skin CAN be an excellent insulator and therefore most of the voltage drop will be across it. – Lenzuola Dec 11 '13 at 6:31
• @xish Of course not. But the external V doesn't matter. The only thing that matters is the voltage drop across your heart, and that DOES depend on your skin's resistance – Lenzuola Dec 11 '13 at 6:32