A question was asked on my midterm the other day and i disagree with the answer given. It was a true or false question, " People become injured and death might occur when voltage pushes electrons through the human body causing the heart to go into ventricular fibrillation." the answer key said true, i said false because it is not the most correct answer, i thought that current pushes electrons and determines the severity of shock. what are your thoughts?
votage or current kills?
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chris kennedy
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If this is a test question the answer could very well be480sparky said:
Contact Resistance
I missed that one in 06.
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The answer is correct...the voltage pushes the current. The amount of voltage, the contact resistance, the points of contact and the internal resistance determine the amount of current that will flow.
don_resqcapt19 said:
I totally agree. When I explain to a new apprentice the difference between amperage and voltage, I use water as a good analogy. Voltage is the pressure and current is the volume. The key to the question is pushes electrons through. Well voltage does push electrons so the answer would be true.
Don also answer is ohms law. I=V/R. With out voltage there is no electrons flowing (current).
cschmid
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Don very good explaination..
ryan_618
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Although the question has been answered already, I think it is worth pointing out that ohm's law (as always) applies. I=E/R. As Don pointed out, the current kills, but the current is the result of a voltage being applied to a resistance, such as your body.
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To the other replies, let me add that "current" is essentially the movement of electrons. Current does not push electrons, current IS electrons (in motion). It is, as others have said, the voltage that does the pushing. But it is the electrons moving through the body (i.e., the curren) that does the damage.kevinjg05 said:
bphgravity
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Is it really the movement of the electrons that kills or is the associated energy?
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Our muscles are controlled by electric signals transmitted by the brain and carried over nerve cells. An exterior source of electric current can override any command from the brain, and take control of our muscles. One effect is that the muscles of your hand, the hand that first touched a live wire, will contract. This can cause your hand to grab the wire more tightly, and force it to disregard the brain's frantic command to let go, since the external current is stronger than the signal from your brain. Another muscle that would be affected by the current is the heart muscle. An external source of current can cause it to disregard all signals from the brain. This will send it into fibrillation, which essentially means that it will flutter uselessly, so that it cannot pump out blood. That, I believe, is the manner in which electric shock can cause death.
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Physis 3
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I'll tell you how it really works. I apologies that I haven't read all the responses but this subject frustrates me immensely and I think it ought to be explained correctly occasionally.
First, this is not a true or false question. It cannot be asked that way.
Current is what kills. This is a fact. somewhere around 20 milliamps, usually it takes more.
But now you have to consider how to get 20 milliamps or more through the body.
Did I say body. That's not accurate either. It's heart.
Well, now you need some Ohm's law. Voltage divided by resistance equals current.
Ever measured a human's resistance. It's around 1 megaohm when you're dry. It can be a lot lower when you're wet. The trouble I have here is that I've seen lots of numbers that don't agree with the measurements in the real world that I've seen. There are several reasons for it. contact surface area is one. More importantly is how wet your skin surface is. even further, is that sweat is saline, or salt water, which is a far better conductor than, say. distilled water.
What the last paragraph means is that you're a variable resister.
Given that you're a resister, and typically a rather high resistance, looking at Ohm's law again, you'll need, usually, a significant voltage to push the current high enough to be fatal.
Let's do some math. If I'm looking to put 20 milliamps through a megaohm the equation for the voltage needed is V=IR , that's voltage equals current times resistance. Or how much voltage is "required" to push a fatal current through a human under typical conditions? The equation is, V = .02 X 1,000,000 = 20,000 or 20,000 volts.
But we know that this isn't true, don't we?
So what are the constants? Just one, current, 20 milliamps, or so.
The variables are both voltage and resistance. Our bodies are constantly at different resistances. How do we control that number? The only value we really have control over is voltage. So given that, we could just as well say that voltage kills. Or we could say that it's voltage that kills because that's what's necessary to push the current. And it definitely is.
And beyond that, you can't separate any one element of Ohm's law and encapsulate it as if the other two don't matter because all three only exist as a single dynamic unit.
I don't like that this is such a standard question and neither the students nor the instructors really understand it. It's not a true or false question!
First, this is not a true or false question. It cannot be asked that way.
Current is what kills. This is a fact. somewhere around 20 milliamps, usually it takes more.
But now you have to consider how to get 20 milliamps or more through the body.
Did I say body. That's not accurate either. It's heart.
Well, now you need some Ohm's law. Voltage divided by resistance equals current.
Ever measured a human's resistance. It's around 1 megaohm when you're dry. It can be a lot lower when you're wet. The trouble I have here is that I've seen lots of numbers that don't agree with the measurements in the real world that I've seen. There are several reasons for it. contact surface area is one. More importantly is how wet your skin surface is. even further, is that sweat is saline, or salt water, which is a far better conductor than, say. distilled water.
What the last paragraph means is that you're a variable resister.
Given that you're a resister, and typically a rather high resistance, looking at Ohm's law again, you'll need, usually, a significant voltage to push the current high enough to be fatal.
Let's do some math. If I'm looking to put 20 milliamps through a megaohm the equation for the voltage needed is V=IR , that's voltage equals current times resistance. Or how much voltage is "required" to push a fatal current through a human under typical conditions? The equation is, V = .02 X 1,000,000 = 20,000 or 20,000 volts.
But we know that this isn't true, don't we?
So what are the constants? Just one, current, 20 milliamps, or so.
The variables are both voltage and resistance. Our bodies are constantly at different resistances. How do we control that number? The only value we really have control over is voltage. So given that, we could just as well say that voltage kills. Or we could say that it's voltage that kills because that's what's necessary to push the current. And it definitely is.
And beyond that, you can't separate any one element of Ohm's law and encapsulate it as if the other two don't matter because all three only exist as a single dynamic unit.
I don't like that this is such a standard question and neither the students nor the instructors really understand it. It's not a true or false question!
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Physis 3
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bphgravity said:
I read some more of the thread now, Hi Bryan, there are two ways to die from electricity. One is being buned to death and the other is the fact that we are electrical gadgets and the signals that trigger our hearts, among other things, can be disabled by electricity.
And electron motion is energy.
Edit: And I just noticed that Charlie B. was on that too. The first part that is.
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Sam,
Sure it can. The question didn't ask what kills...the question only asks if the votlage pushes the current. That is the common description to how electric circuits work and applies to circuits involving humans as well as those involving wire.
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Physis 3
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You're right. :grin: I was just automatically thinkin g of the current kills version.
zog
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"And electron motion is energy"
Right, current is the transfer of energy from molucule to molucule, not the flow of electrons, electrons dont move much the energy transfer moves at near the speed of light.
No one has mentioned duration, IEC 479 data shows the affect of duration which is vital to discuss when talking about the affect of current on the human body, 20mA wont kill you unless the duration is long which is possible because 20mA causes a loss of muscle control (Contracting for AC) which can cause you to become "stuck" on a circuit.
Right, current is the transfer of energy from molucule to molucule, not the flow of electrons, electrons dont move much the energy transfer moves at near the speed of light.
No one has mentioned duration, IEC 479 data shows the affect of duration which is vital to discuss when talking about the affect of current on the human body, 20mA wont kill you unless the duration is long which is possible because 20mA causes a loss of muscle control (Contracting for AC) which can cause you to become "stuck" on a circuit.
hockeyoligist2
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I remember a post, long time ago, that someone was killed by a Fluke meter. Anyone have a link to that?
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Physis 3
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480sparky said:
I was almost gonna give you that one until it occured to me that gravitation, and smashing the planet with yourself would be responsible there. :grin:
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