Please explain this short text on electricity from my physics book.?

Question

"The EMF of a charged Van de Graaff generator, or any source of high voltage, can be estimated from the length of the
spark it will produce. Between smooth spheres, in dry air, a spark will jump about 1 cm for every 25 000 V. Between
pointed conductors it will jump 1 cm for every 10 000 V. Under good conditions a Van de Graaff generator might produce a
spark of up to about 15 cm, that corresponds to nearly 400 000 V."

If you've read the above quote you can understand that huge voltages are associated with a Van de Graaff generator. Then why is it that the effect of one of these contraptions on the human body is 0, while the effect of putting your hand in a toaster (ie. 240 V) is potentially lethal?

Answer 1

Hmmm an interesting question: A Van de Graaff generator does produce voltages in excess of 400,000 volts; those that are found in schools. However they are NOT lethal for two main reasons.

First the Van de Graaff stores charge on the sphere and that is limited and depends on the humidity and smoothness of the sphere. School units don;t store much charge (energy).

When you come near or actually touch the Van de Graaff charge very rapidly flows from the sphere onto your body. However, since the charge is limited that actual time is very short and the apparent frequency very high. At high frequency, (very rapid change in voltage) the current (charge per unit of time) travels overthe surface of your body. This fact is verified by high voltage Tesla coils that put out voltages in excess of 500,000 V at 500 KHz. I have touched such an out put from a Tesla coil without feeling any shock at all. The current at 500 kHz flowed over my skin harlessly into the ground. The Van de Graaff just generates the one pulse of charge and similarly you do feel a tingle but mostly its due to the effect at the area where the charge enters your body. If you approach a Van de Graaff with a sharp pin in your hand and make it the closest part of you to the Van de Graaff you will not feel any shock at all. It is possible to make a Van de Graaff lethal. Storing the charge generated can increase the energy available and with enough storage it could prove fatal.

Hope these comments help

Answer 2

By the way your question is asked I believe you may not fully understand the nature of electricity. the Van de Graaff generator builds up a massive potential (Voltage) at a very low rate of Amps. power is equal to voltage multiplied by ampeage and is measured in Watts. A toaster has a massive amount of power in comparison to a Van de Graaff generator.
The best way to think of electricity is the old waterpipe rule.
The voltage is the pressure that pushes the water.
The water itself is the current
The size of the pipe is the resistance.
The amount of water is dependant on the amount of water in the pipe and the pressure.
You can increase the water pressure by putting the same amount of water through a smaller pipe, but the amount of water stays the same, i.e. when you transform electricity you change the voltage up and the amps will fall, vice versa.
By the way electricity hates water in nature, small amounts of electricity will have a huge effect if you are wet.
hope this helps.

Answer 3

The difference is the amount of current generated.
Not much current is generated in a Van de Graff generator but there is a lot of current in a home electrical system.

High voltage at low current can stop your heart but high current at any voltage will cook you due to heat generated as a lot of electrons pass through your body.

Answer 4

this is talking about how an electric charge can travel accross air. It would really depend on how clean your air is (it's more than just oxigen) but your hand is a better conductor, plus the charges on the toaster are distributed, to get the toaster hot and not to make a spark just jump from one side to the other.

;-)

Answer 5

well with a van de graaf generator usually the person is grounded ie standing on a milk crate or something so he isn't touching the ground so to speak and complete a path for the electircity to travel through him, and also remember it isn't voltage that kills you it's the amps, you only need .1A i think for it to be lethal.

As far as a toaster goes that's running off of regular house electricty from the power lines which is 120 V and i can't remember off the top of my head how many amps but i know it's in the 10's of amps or higher i can't really remember hope that helps you answer your quesiton

Answer 6

It probably has something to do with the amperage of the toaster, which is not listed as a variable in the problem. High voltage can cause your heart to stop beating, requiring CPR to restart it. High amperage will burn you, which takes time to heal. Since V=I*R then V/R=I. Given 100k ohms of resistance in the human body, I=25000/100000=0.25 amps, which is not a lot. I really don't think putting your hand in a toaster will kill you, but the heat will burn you.

Answer 7

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