By Tabish

2012-09-14 20:01:26 8 Comments

Though voltage and current are two interdependent physical quantity, I would like to know what gives more "shock" to a person - Voltage or Current? In simple words, will it cause more "electric - shock" when the voltage is high or Current is more?


@Farcher 2019-10-16 10:20:41

It cannot be just voltage as you can demonstrate with a comb!

After a comb has been passed through dry hair it acquires a charge which can be shown by the comb picking up small pieces of paper which are close to it.
The potential of part of the comb relative to the holder of the comb is actually very large and can be thousands of volts.
This can be shown by using a (gold) leaf electroscope as a voltmeter which deflects if the applied voltage is greater than hundreds of volts.
Bringing the charge comb close to the electroscope will give a sizeable deflection.

If the holder of the comb touches the charged end then he/she will not feel a shock the reason being that although the voltage is high the charge on the comb is so small that when transferred to the holder the resulting current is very small.

A small electrostatic generator called an electrophorus when charged and touch can produce a tingling sensation and also sometimes a small spark, in the act of the electrophorus being touched, which can be hear and seen in a darkened room.

Still a high voltage but with more charge transfer, ie a larger current, results in a greater response by the human body.

So it is the current, the result of the applied voltage and the resistance of the human body, (and the time of contact) which determines how the human body reacts.

This table shows the relationship between effect and current although the quoted currents are approximate values.

enter image description here

The variability of data is shown by the fact that humans have been electrocuted with a voltage as low as $40\,\rm V$ and at the other extreme a man survived with making an electrical circuit touching a $340\,000 \,\rm V$ transmission line.

The Wikipedia article Electrical Injury gives more information about such matters as does the article The Fatal Current.

@user21000 2013-02-15 18:19:28

the current generates the heat.....but the voltage (potential difference) generates i think shock is generat due to high voltage!!

@Waffle's Crazy Peanut 2012-09-15 02:05:19

You see, current in one direction indicates the flow of free electrons in the other direction. Hence, current flows. But voltage does not flow. It's actually the work done per unit charge. (Joule/Coulomb). In other words, it's an energy or simply the potential difference between two points. Sometimes, a bird does not get a shock while resting on a carrier wire (Not all time the bird sits on the same wire). Whereas By touching the live wire and ground, we create a potential difference (a path which is sufficient enough for current to flow) with live wire relative to earth. Hence, we get a shock...

Electric shock is the sufficient amount of current flowing through human body which the person could feel. But, this doesn't mean that shock is not caused by Voltage. Of course, it depends upon voltage which is given by Ohm's law... $$I=\frac{V}{R}$$

The shock your body feels, depends upon the applied voltage & resistance of your body. If your body has a resistance of about 10,000 $\Omega$, and the voltage is 230 V, then $$I=\frac{230}{10000}=23 mA$$

You would get a shock, but seriously... (You can't let go off this current)

Hence, you cannot differentiate a shock based on voltage or current. It depends on both voltage and resistance of your body (which implies current).

Here's a page which shows current paths and another one which provides comparison info..!

@endolith 2016-06-02 18:00:28

"You see, current in one direction indicates the flow of free electrons in the other direction." No, conventional current indicates a flow of positive charge. In metals, this consists of a flow of electrons in the opposite direction. In your body, it consists of positive and negative ions flowing in opposite directions at the same time.

@Jaime 2012-09-14 21:59:17

You'd have to define 'shock', but what kills you is enough current during enough time, not voltage. Of course you need enough voltage to keep the current going over your body's resistance, but it definitely plays a secondary role.

In a former professional life I worked developing Residual Current Circuit Breakers, and 30 mA is the usual rating for devices aiming at protecting lives. In wet environments, such as bathrooms or swimming pools, sometimes 10 mA is recommended.

According to wikipedia's RCCB article, 25-40 ms of 30 mA is enough to send your heart into fibrillation, which probably qualifies as a pretty strong shock. That would require your heart being in the path of the current, though. This link has more information on what to expect depending, again, on the current, not the voltage.

@anna v 2012-09-15 04:22:17

I suggest this is self evident. You can have a high voltage between two metal plates and put your hand through safely as long as you do not touch them. Otherwise nobody would be able to repair fuses so close to live wires. If there is no current there is no damage, it is the current we feel as "shock".

@Alfred Centauri 2012-09-15 21:43:29

@annav, this problem is in the context of a circuit which implies a closed path for a current to exist. While I appreciate the point you've made, I believe it is actually out of context as there is no circuit in your example.

@BlackThorn 2018-04-06 16:54:55

"it definitely plays a secondary role." Since voltage and current are proportional, I fail to see how you can assert that one is more important than the other.

@Jaime 2018-04-06 23:40:25

They are proportional in a constant resistance setting. A relatively low voltage can give you a big shock if your hands are e.g. wet, since current will be higher then. Conversely, a not that low voltage may go unnoticed if it prices no current, e.g. because you are wearing non conductive shoes.

@Alfred Centauri 2012-09-14 21:43:55

If we model the path for the current through the human body as a resistor, then by Ohm's law, the current and voltage are proportional.

That is, a greater current through the body will be associated with a greater voltage across the body.

Having said that, let's consider the source of the shock. It is the case that sources may produce a large voltage but are not capable or sourcing significant current. These sources are said to have high internal resistance.

The point is that a high-voltage source with high internal resistance may not give you much of a shock at all while a lower voltage source with low internal resistance may kill you.

So, there really isn't a simple answer to your question other than "it depends".

@Anixx 2012-09-14 20:37:24

Higher voltage causes more shock at the same wattage.

Low-voltage high-current exposure will be felt as warming up not as a shock.

@Ron Maimon 2012-09-14 20:16:11

The shock is the product of the current and the voltage, so in principle you need both. A friction spark from your shoe is high voltage by low ampage, but a shock from a power main is high ampage and comparatively low voltage.

The type of current, whether it is alternating or steady, is also important, as an alternating current will interfere with biological processes more than a steady current. But the energy deposited is the product of the two, so it is not meaningful to separate them out.

@Tabish 2012-09-14 20:17:54

Thanks for your quick response Ron but I would like to understand two more points on this : 1. When a bird sits on high voltage wire, nothing happens - of course the conductivity is not there so in spite of high voltage there is no "electric-shock".. Doesn't that suggest "Voltage" has no role in the intensity of the "shock" ?

@Tabish 2012-09-14 20:24:02

2. When you say "shock is the product of the current and the voltage", do you say this is how we can quantify the intensity of "shock" ? Is this the actual formula ?

@Ron Maimon 2012-09-14 20:33:26

@Tabish: For the first thing, by voltage, one always means "voltage difference", the bird has no voltage difference between it's feet, so there is no effect. The product is the energy delivered by the shock, so it's how much you heat up, how much burning you get at the skin and flesh, but it isn't the severity of stopping your heart, which is a different thing, related to the electrical flows that regulate the heartbeat. Also, in terms of feeling the shock, setting up nerve impulses is not by power, but by the change in intermembrane voltages, but power is good rough guide to the effect.

@Tabish 2012-09-14 20:36:06

Thanks Qmechanic, It helped. Thanks Ron for taking time to address this.

@endolith 2013-05-11 04:27:05

"A friction spark from your shoe is high voltage by low ampage" No, it's several amps. It's harmless because of the short duration.

@Ron Maimon 2013-05-12 16:19:10

@endolith: You know what I meant, I meant "charge delivered", so you get the energy out when you multiply.

@endolith 2013-05-13 14:19:58

@RonMaimon: Usually when people say "static electrical discharges are low current", they actually believe that they are low current, and that that is what makes it harmless. This leads to sayings like "it's the current that kills, not the voltage". Static discharges are harmless because the current is short-lived, not because it is low.

@Ron Maimon 2013-05-13 16:54:51

@endolith: You are completely right of course, I wasn't thinking about nuances, I just wanted to explain the energetics is the product of the charge times voltage difference, and I used P=IV. I don't want to bump this, but if you feel strongly, edit the answer as you like.

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