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Electricity and the Earth

by quietrain
Tags: earth, electricity
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quietrain
#1
Feb2-11, 10:42 PM
P: 651
i was pondering over a few questions

1) if i were to connect a wire from the positive of a power source, and touch the other end to myself, would i get electrocuted? common sense tells me i will, but where is the close circuit? does electricity flow from source to me to the earth? and then how does it get back to the source to form the complete circuit?

2) if electrons were the moving charges in electricity, then how does it come out of the positive source ? does it mean that the earth's electrons are the ones moving into the positive source? so i should feel the shock at my feet first and not at my hands touching the source point?

3) what if i were to shield myself from the earth, like maybe jump up, or be in space where that is no earth. then if i touch the postive source, will i get electrocuted? where is the complete circuit?

4) if now i were to dig myself into the earth. since by gauss law, all charges resides on the surface of the earth, then if i were to touch the source again, will i be electrocuted? since no charges are inside? the power source is essentially neutral right? so i will not get a cavity inside a sphere with balanced induced charges from the earth.

5) now if i were to put a +ve charge huge enough into a cavity in earth to attract all the electrons in the earth to balance it, then all the outer postive charges will be able to move freely, and does it mean it will start to electrocute everyone on earth?

6) also, when we talk about earthing, if we keep taking electrons out from the earth, when willl the earth run out of it? and since electron can flow freely into and out of earth, does it mean that earth is a good conductor of electricity? but i though metals are with free electrons, earth is mainly soil and water right?

7) also when earthing, if i keep electrons off it, wouldn't the earth get charged up?

thanks!
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quietrain
#2
Feb4-11, 10:03 PM
P: 651
anyone?
Gigasoft
#3
Feb5-11, 03:40 AM
P: 59
Quote Quote by quietrain View Post
i was pondering over a few questions
1) if i were to connect a wire from the positive of a power source, and touch the other end to myself, would i get electrocuted? common sense tells me i will, but where is the close circuit? does electricity flow from source to me to the earth? and then how does it get back to the source to form the complete circuit?
Only if you are connected to something which is connected to the negative wire.

2) if electrons were the moving charges in electricity, then how does it come out of the positive source ? does it mean that the earth's electrons are the ones moving into the positive source? so i should feel the shock at my feet first and not at my hands touching the source point?
They don't. The direction of movement is into the positive source. And the direction of propagation of field changes is completely unrelated to the electrons' direction of movement. The current is established almost instantaneously, so you will feel the shock at the feet and your hands at the same time.

3) what if i were to shield myself from the earth, like maybe jump up, or be in space where that is no earth. then if i touch the postive source, will i get electrocuted? where is the complete circuit?
You will acquire a charge such that you end up at the same potential as the source. Unless the difference was at thousands of volts, you will hardly feel anything if at all.

4) if now i were to dig myself into the earth. since by gauss law, all charges resides on the surface of the earth, then if i were to touch the source again, will i be electrocuted? since no charges are inside? the power source is essentially neutral right? so i will not get a cavity inside a sphere with balanced induced charges from the earth.
Yes, as long as the source itself is not touching the earth, you will be electrocuted.

5) now if i were to put a +ve charge huge enough into a cavity in earth to attract all the electrons in the earth to balance it, then all the outer postive charges will be able to move freely, and does it mean it will start to electrocute everyone on earth?
Yes, and it would also destroy the entire solar system.

6) also, when we talk about earthing, if we keep taking electrons out from the earth, when willl the earth run out of it? and since electron can flow freely into and out of earth, does it mean that earth is a good conductor of electricity? but i though metals are with free electrons, earth is mainly soil and water right?
At a rate of 1A, it would take approximately [tex]1.817\times10^{25}[/tex] years. In an electrolyte, electricity is conducted by ions.

7) also when earthing, if i keep electrons off it, wouldn't the earth get charged up?
Yes, but I don't see where you plan to store all these electrons.

Studiot
#4
Feb5-11, 04:13 AM
P: 5,462
Electricity and the Earth

1) if i were to connect a wire from the positive of a power source, and touch the other end to myself, would i get electrocuted? common sense tells me i will, but where is the close circuit? does electricity flow from source to me to the earth? and then how does it get back to the source to form the complete circuit?
Possibly. DO NOT TRY THIS WITHOUT SUPERVISION.

Small capacity (batteries) and/or low voltage sources are fairly safe, although you could get quite a nip from the 90volt positive terminal of an old fashioned HT battery for valve apparatus.
quietrain
#5
Feb6-11, 03:34 AM
P: 651
Quote Quote by Studiot View Post
Possibly. DO NOT TRY THIS WITHOUT SUPERVISION.

Small capacity (batteries) and/or low voltage sources are fairly safe, although you could get quite a nip from the 90volt positive terminal of an old fashioned HT battery for valve apparatus.
possibly? you mean that there is no certain answer to the first question? because i can't find the complete loop for electrons to flow assuming i insulate myself from the ground, but i know i will get electrocuted :( doesn't make sense.
quietrain
#6
Feb6-11, 03:48 AM
P: 651
Quote Quote by Gigasoft View Post
Only if you are connected to something which is connected to the negative wire.
erm, so you mean that if i were to touch the +ve live wire in the socket with my finger i won't die? since i am not connected to the negative wire?

Quote Quote by Gigasoft View Post
They don't. The direction of movement is into the positive source. And the direction of propagation of field changes is completely unrelated to the electrons' direction of movement. The current is established almost instantaneously, so you will feel the shock at the feet and your hands at the same time.
oh but it comes from earth then feet up right?

Quote Quote by Gigasoft View Post
You will acquire a charge such that you end up at the same potential as the source. Unless the difference was at thousands of volts, you will hardly feel anything if at all.
so the moderm day power socket is about 240v, and human resistance is about 1k ohms? so 240 / 1000 = 0.24A is this enough to kill? i read somewhere it says 0.2 A is enough to make your heart go haywire :(

Quote Quote by Gigasoft View Post
Yes, as long as the source itself is not touching the earth, you will be electrocuted.
but why? you mean if i were to touch the source and the earth now, electrons from the outer surface of the earth would flow through me into the source so as to balance the potential difference? then wouldn't that mean that the earth gets charge up now? so i just need to have a potential step up to extremely high values in the earth so that if i connect a wire from it to the earth, i literally absorb the electrons and earth gets charged?

Quote Quote by Gigasoft View Post
Yes, and it would also destroy the entire solar system.
:O
well ok, lets say now i put a charge that is not big enough to kill everyone and the solar system but enough to free some electrons on the surface of the earth then i could still get earth to charge up right?

Quote Quote by Gigasoft View Post
At a rate of 1A, it would take approximately [tex]1.817\times10^{25}[/tex] years.
er how do we know it would that take long?

Quote Quote by Gigasoft View Post
Yes, but I don't see where you plan to store all these electrons.
well , i am thinking if we could leave all the earth surface charged, then wouldn't i be able to connect wires to space installations and send electricity with near infinite electricity? since the earth takes so long to lose all its charges !

and now, thinking further, if i am able to use something else that conducts electricity besides wires, like maybe air when it reaches breakdown potential, then i could literally send jets of electricty outwards from earth to maybe kill impending asteroids or aliens :X
Studiot
#7
Feb6-11, 06:06 AM
P: 5,462
I repeat my safety warning.

You asked if your would be electrocuted and later if you would die.

To which I replied possibly because the severity of the effect would depend upon the capacity of the supply and the quality of your insulation from ground.

You can safely tough the positive (or more likely negative) terminal of a Van Der Graff gnerator at 250,000 volts if you are well insulated from earth because the capacity is low and the insulation is good.

But if you touched the +200V terminal of a (very) old fashioned DC mains supply you would probably be electrocuted. DC supplies are inherently les safe than AC because once grasped, you cannot let go of a DC one.
quietrain
#8
Feb6-11, 06:32 AM
P: 651
Quote Quote by Studiot View Post
I repeat my safety warning.

You asked if your would be electrocuted and later if you would die.

To which I replied possibly because the severity of the effect would depend upon the capacity of the supply and the quality of your insulation from ground.

You can safely tough the positive (or more likely negative) terminal of a Van Der Graff gnerator at 250,000 volts if you are well insulated from earth because the capacity is low and the insulation is good.

But if you touched the +200V terminal of a (very) old fashioned DC mains supply you would probably be electrocuted. DC supplies are inherently les safe than AC because once grasped, you cannot let go of a DC one.
weird, i read a number of post online and some say ac is worse, some say dc is worse assuming equal voltages

they say ac cause burns jerks etc while dc make uninterrupted continuos flow

some say ac is alternating so safer, but some say the alternating is the one that kills because of jerks ... :(

oh well ... thanks anyway!
Naty1
#9
Feb6-11, 10:59 AM
P: 5,632
1) if i were to connect a wire from the positive of a power source, and touch the other end to myself, would i get electrocuted? common sense tells me i will, but where is the close circuit? does electricity flow from source to me to the earth? and then how does it get back to the source to form the complete circuit?

Think about the lightning strike version of this. If the voltage in your question is high enough it can jump from you to earth...which is essentially and infinite sink....
In fact some power generation uses positive voltages on lines and uses the earth as the "return".



2) if electrons were the moving charges in electricity, then how does it come out of the positive source ? does it mean that the earth's electrons are the ones moving into the positive source? so i should feel the shock at my feet first and not at my hands touching the source point?

When electricity was first discovered, experimentalists assumed it was a positive charge so thats the conventional direction still used today...way back then the electron had not been disocovered....actual current flows opposite to conventional flow.

3) what if i were to shield myself from the earth, like maybe jump up, or be in space where that is no earth. then if i touch the postive source, will i get electrocuted? where is the complete circuit?

see my answer to (1)..can there be a "spark" form you to earth???
quietrain
#10
Feb6-11, 11:25 PM
P: 651
oh so you mean ionization of the air? so that electricity leaps off me through the air and into the earth?

now, what if i insulate myself in a box , if i touch the positive terminal of a source, will i get shock?
gigasoft mentioned earlier that i would just get the same potential as the source.

so does this mean that electricity does not need a close loop to flow? since the charges have to flow into me, for me to have the same potential as the source. there is no close loop at all.

in a sense i became an extension of the conducting source?

so if that is the case, why when we connect a resistor or capacitiy to just the positive terminal of a source, there is no current measured?
Studiot
#11
Feb7-11, 03:55 AM
P: 5,462
I am sorry I seem to be wasting my time, as you only listen to what you want to hear....

If you genuinely believe you can#t get a shock by touching only one terminal of a DC source, explain why some people experience shocks from touching door knobs.
quietrain
#12
Feb7-11, 11:36 PM
P: 651
Quote Quote by Studiot View Post
I am sorry I seem to be wasting my time, as you only listen to what you want to hear....

If you genuinely believe you can#t get a shock by touching only one terminal of a DC source, explain why some people experience shocks from touching door knobs.
well, thats the whole point i am asking. where is the close loop? i can't find the close loop for electricity to flow.

i never said i believe i won't get a shock, thats why i am seeking answers here. but in your post you only keep telling me that i will be shocked, but how? why? and now you ask me to explain my own question about why people get shock??? if i knew, i wouldn't be wasting my time asking here :(
Studiot
#13
Feb8-11, 05:28 PM
P: 5,462
You actually asked 7 questions originally, and later tried to impose all sorts of trick conditions.

In my opinion that is not the way to understanding.

I actually only addressed the first of your questions and only for safety reasons.
However, since no one else seems to want to try to untangle your issues here is more.

There is no requirement that a 'circuit' be present for charge to move. A circuit may be present and this allows us to deduce certain useful circuit laws.


Charge can move or be moved on or in a body.
Charge can collect or be collected on or in a body.

The ease or difficulty of these processes basically take up most of the theory of electricity and depends upon many factors. The usual starting point for this is called electrostatics or static electricity - a bit strange really since the charge actually does move.

If we start with a system where everything is neutral or uncharged everywhere we can cause or allow this to change by causing or allowing charge to move and collect at certain places in our system. The system remains neutral overall because there is no external source of charge or external place for charge to leave the system to (a sink).
This may sound a pompous mouthful, but consider my doorknob example.

A neutral person walks across a nylon carpet in dry conditions.
In doing this some charge is transferred from the carpet to the person, who is no longer neutral.
This charge spreads out over the surface of the person, but cannot go further because the environment is dry and insulating. The nylon carpet itself is insulating and prevents the charges going to the floor underneath.
When the person reaches the door he reaches out and touches the metal knob.
Because the knob is conductive compared to the person, most of the charge collected by that person is rapidly transferred to the knob and is felt by the person as a (small) shock.

Each transfer of a small amount of charge from the carpet to the person is also a very small shock, but not perceived because it is a small change over a relatively long timescale.
This is why the person perceives the discharge process as a shock, but not the charge.
davenn
#14
Feb8-11, 07:47 PM
Sci Advisor
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davenn's Avatar
P: 2,463
Quote Quote by studiot
Charge can move or be moved on or in a body.
Charge can collect or be collected on or in a body
Indeed....
quietrain, go watch some youtube videos of guys moving off helicopters onto 220kV transmission lines watch the huge discharge between the transmission line that the probe rod the guy uses to get to the same potential as the line

Quote Quote by studiot
Each transfer of a small amount of charge from the carpet to the person is also a very small shock, but not perceived because it is a small change over a relatively long timescale.
This is why the person perceives the discharge process as a shock, but not the charge
and also because the transfer of charge is not directly against the sensitive skin, as in the discharge to the doorknob through the fingertips, rather it is over a wide area of the soles of the shoes :)

Dave
quietrain
#15
Feb8-11, 10:37 PM
P: 651
Quote Quote by davenn View Post
Indeed....
quietrain, go watch some youtube videos of guys moving off helicopters onto 220kV transmission lines watch the huge discharge between the transmission line that the probe rod the guy uses to get to the same potential as the line

Dave
are you talking about this video? http://www.youtube.com/watch?v=9tzga...eature=related
i don't really understand what hes doing here

when he takes the probe rod and place near the transmission cable, there is electricity, but it looks fake? or is it real?

also, i assume the transmission cable is insulated? then how does charge fly out? or in?

anyway, so if charges are transferred, so that they are at same potential, so its the suit that he is wearing that is at the same potential? but he is insulated from the suit inside so he does not get the charges?

so when he wants to take something from the helicopter, he needs to zap the helicopter to be at the same potential so no electricity transfers? but since zapping also transfers charges, then why don't he just take directly? the helicopter is not grounded either?
quietrain
#16
Feb8-11, 11:09 PM
P: 651
Quote Quote by Studiot View Post
You actually asked 7 questions originally, and later tried to impose all sorts of trick conditions.

In my opinion that is not the way to understanding.

I actually only addressed the first of your questions and only for safety reasons.
However, since no one else seems to want to try to untangle your issues here is more.

There is no requirement that a 'circuit' be present for charge to move. A circuit may be present and this allows us to deduce certain useful circuit laws.


Charge can move or be moved on or in a body.
Charge can collect or be collected on or in a body.

The ease or difficulty of these processes basically take up most of the theory of electricity and depends upon many factors. The usual starting point for this is called electrostatics or static electricity - a bit strange really since the charge actually does move.

If we start with a system where everything is neutral or uncharged everywhere we can cause or allow this to change by causing or allowing charge to move and collect at certain places in our system. The system remains neutral overall because there is no external source of charge or external place for charge to leave the system to (a sink).
This may sound a pompous mouthful, but consider my doorknob example.

A neutral person walks across a nylon carpet in dry conditions.
In doing this some charge is transferred from the carpet to the person, who is no longer neutral.
This charge spreads out over the surface of the person, but cannot go further because the environment is dry and insulating. The nylon carpet itself is insulating and prevents the charges going to the floor underneath.
When the person reaches the door he reaches out and touches the metal knob.
Because the knob is conductive compared to the person, most of the charge collected by that person is rapidly transferred to the knob and is felt by the person as a (small) shock.

Each transfer of a small amount of charge from the carpet to the person is also a very small shock, but not perceived because it is a small change over a relatively long timescale.
This is why the person perceives the discharge process as a shock, but not the charge.
i am sry but in my opinion, asking questions is the way to understanding. questions arise when you practise and practice makes perfect.

and if no one wants to answer my questions , then perhaps i have asked a complicated one , or it is just plain dumb. in any case, i don't see why i should be discouraged to ask questions.

and if i udnerstand what you are saying, that means if i were to connect a +ve source only to a light bulb , i would get an instantaneous flash as both potential become the same, i.e charges flow from source to bulb. but it ends when no more charges flow and potential are the same.

so if i were to add a connection to the earth and use a mechanical device to create the source electricity, like charging glass with fur, then i would be creating electricity?

so now i am thinking is there a way to maintain a constant potential? like maybe tap the sun's energy? but i don't know how to translate heat energy to electric potential energy :(
russ_watters
#17
Feb8-11, 11:20 PM
Mentor
P: 22,224
It's only been half an hour. You need to be patient. Some of the easier answers:

Yes, it is real. No a transmission line is not insulated. It's the suit and the helicopter that get charged. No, he doesn't get charged and no, he's not insulated from the suit - people have higher resistance than a metal suit, so electricity won't flow through us when we're wearing a meatal suit. No, the helicopter isn't grounded - it's hovering!
JaredJames
#18
Feb8-11, 11:36 PM
P: 3,387
Quote Quote by quietrain View Post
well, thats the whole point i am asking. where is the close loop? i can't find the close loop for electricity to flow.

i never said i believe i won't get a shock, thats why i am seeking answers here. but in your post you only keep telling me that i will be shocked, but how? why? and now you ask me to explain my own question about why people get shock??? if i knew, i wouldn't be wasting my time asking here :(
Because you're earthed. You don't need to 'close the loop' so far as a physically wired circuit goes.

When you touch a live terminal the current flows through you into the ground (or whichever path is easiest).

Think of a lightning strike on a lightning conductor. It strikes near the top and flows away, dissipating in the ground below. It's the same basic principle as touching a live terminal, AC or DC.

In comparison, if you wear really thick rubber shoes you could probably grab a live terminal and experience no shock at all. I wouldn't try that though.


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