Homework Help: At the atomic level why is it harmful to stand in an electric field?

1. Aug 9, 2014

needingtoknow

1. The problem statement, all variables and given/known data

I was reading on Faraday's Cage and how if we are inside a conductor (car) we will not be harmed by the electric field strength of lightening if it strikes the car. (because conductors always have an E = 0 inside them because excess charge will always rapidly move to the surface in an attempt by electrons to repel each other) So obviously electric fields are harmful but why? Is it because we have dissolved free ions inside of us that can interact with the electric field?

2. Aug 9, 2014

SteamKing

Staff Emeritus
No, that's not it. If your body acts as a lightning rod, it can suffer serious burns and disruption of the electrical activity in the brain, central nervous system, and heart. In essence, it's like getting a big shock. If your heart stops beating or your brain gets literally fried, you die. End of Story.

The Faraday Cage provides an alternate path for the electricity in the lightning bolt to go to ground, so that it doesn't pass thru your body.

3. Aug 9, 2014

needingtoknow

But isn't gravity analogous to electrostatic force? An electric field is composed of a collection of vectors. So what happens when electric field vectors strike a person? Why isn't that the same as let's say putting one object at Point A and another at Point B and then standing in the middle? In this case just with electrostatic force you are standing in the middle of the gravitational field created by the objects at Point A and Point B right?

4. Aug 9, 2014

matineesuxxx

I don't know too terribly much about electricity, however coulombs law follows the same inverse square law as the gravitational force, but it is much, much stronger than gravity, and so your example of standing between two uncharged bodies A and B is not really comparable.

Say you have two masses, $m_A$ and $m_B$ and two charged particles $q_1$ and $q_2$ where $|m_A| = |q_1|$ and $|m_B|=|q_2|$, and the distance between $m_A$ and $m_B$ is the same as the distance between $q_1$ and $q_2$. The force of gravity between $m_A$ and $m_B$ does not even begin to compare to the magnitude of the force between $q_1$ and $q_2$. The distance between the two masses would have to be extremely small.

Last edited: Aug 9, 2014
5. Aug 9, 2014

SteamKing

Staff Emeritus
Electric field vectors are mathematical constructs. You would probably suffer more serious injury if a person dropped a math textbook on your head.

A lightning bolt is the flow of electricity where the charge has built up to such a level that the atmosphere no longer acts as an insulator between two regions of opposite polarity, which then are able to neutralize.

Because your body is not that great a conductor of electricity, the flow of electricity thru it as the result of a lightning strike will cause heat to be generated in the tissues, which can lead to burns.

The disruption of electrical activity in the heart can cause that organ to lose proper function, which must be treated properly to prevent serious injury to other organs or death if proper blood flow cannot be restored. A defibrillator is a device which applies a controlled electric shock to an improperly functioning heart to establish a normal heart rhythm.

There are cases where a person struck by lightning may emerge from the experience changed neurologically: the person may speak with a foreign accent, or, in rather rare cases, speak in a foreign language while apparently having lost the ability to speak or understand his or her native language:

http://www.telegraph.co.uk/news/wor...r-wakes-from-coma-speaking-fluent-German.html

Van de Graaf generators can accumulate static charges which may have a potential difference of thousands of volts w.r.t. ground, but because there is no discharge possible, the biological effects in humans are relatively benign, if not comical:

6. Aug 9, 2014

Staff: Mentor

Setting masses equal to charges does not make sense, at least at the level of this question.
You can use particles like electrons and protons - the precise answer will depend a bit on the chosen particle, but the electromagnetic interaction is stronger by a factor of about 10000000000000000000000000000000000000000.

@needingtoknow: Electric fields in a body lead to a current (and indeed, the dissolved ions contribute to this), and this can destroy cells due to heat or uncontrolled ion/electron flows where they can be harmful (cause muscle contractions, erratic signals in neurons, ...).
Gravity is not strong enough to produce anything similar.

7. Aug 9, 2014

matineesuxxx

This was exactly my point, I think its just easier to understand just how much stronger it is than gravity by choosing an example such as this - where the only thing numerically different about the two equations are the different constants.

Last edited: Aug 9, 2014