Electricity Questions

[Chesterton]

1. There are AC outlets in my house. When I plug a cord into them the electrons flow into the cord. Where do the electrons go when the plug is not plugged in? Do they make a round trip back to their source?

2. If I'm in a small amount of water, like a bathtub, and drop an AC powered appliance into it, I'll likely be electrocuted to death. I assume that if I were in a larger amount of water, such as a lake, I wouldn't be. Is there a mathematical formula to express how electricity disperses through water? (I recall that there is some formula to express the dispersion of light.)

3. If I'm in a bathtub, and drop a battery powered (DC) appliance into it, would I get electrocuted the same as with an AC appliance plugged into the wall?

 

[TheBear]

Electrocuted to death is bad. It'll ruin your day. That's for sure.

 

[GenetoJean]

1. There are AC outlets in my house. When I plug a cord into them the electrons flow into the cord. Where do the electrons go when the plug is not plugged in? Do they make a round trip back to their source?

Its kind of like a waterhose, if it isnt used electricity doesnt go anywhere. The controls at power stations can sense that electricity isnt being used as much and then creates less electricity.

2. If I'm in a small amount of water, like a bathtub, and drop an AC powered appliance into it, I'll likely be electrocuted to death. I assume that if I were in a larger amount of water, such as a lake, I wouldn't be. Is there a mathematical formula to express how electricity disperses through water? (I recall that there is some formula to express the dispersion of light.)

I dont think there is. I think that the path of electricity through a large amount of water has way too many factors to be able to make a formula.

3. If I'm in a bathtub, and drop a battery powered (DC) appliance into it, would I get electrocuted the same as with an AC appliance plugged into the wall?

Typically no but that is because DC typically works at voltages a lot lower than AC. On the other hand, if you are comparing similar voltages DC can actually do more damage.

 

[florida2]

Despite popular belief, it is not actually the water than conducts electricity. Rather, it is impurities in the water (such as salts) which are the conductors. Pure water is a terrrible conductor.

I'm not sure about the size of the body of water - probably to due with resistance the further the electricity has to travel.

 

[Embedded]

1. There are AC outlets in my house. When I plug a cord into them the electrons flow into the cord. Where do the electrons go when the plug is not plugged in? Do they make a round trip back to their source?

When you plug in, say a lamp with a switch... if the switch is off then the the electrons do not flow anywhere. because the circuit is still 'open.' When you turn the lamp on the circuit is now 'closed' (yes it is a bit counter intuitive) and the electrons will then flow back and forth (AC) through the filament of the lamp.

Other strange thing is that while switching on the lamp is almost instantaneous (practically speaking it IS instantaneous) the electrons themselves do not move very fast. They flow in one direction at about 84 meters/second max in a 12 gage wire carrying 10 Amperes. But they only do this for half a cycle then they flow back at the same speed. Doing some back of envelope math says they will travel about 0.7 meters back and forth. It is unlikely that any given electron in the lamp itself will ever leave the lamp cord if it is 1 meter long.

So... when the cord is not plugged in they go nowhere. When something is plugged in and off, they go nowhere. When something is plugged in and turned on they go a short distance back and forth. In AC circuits thy do not make a 'round trip.' I a DC (direct current) circuit they do make a 'round trip.'

2. If I'm in a small amount of water, like a bathtub, and drop an AC powered appliance into it, I'll likely be electrocuted to death. I assume that if I were in a larger amount of water, such as a lake, I wouldn't be. Is there a mathematical formula to express how electricity disperses through water? (I recall that there is some formula to express the dispersion of light.)

Pure unionized water has much higher resistance than you. Dropping a hair-dryer (that is plugged in) in to the bath tub will connect the current from the wall socket to the water in the bath. The electric current will 'spread out' through all the water AND you, and will take the path of least resistance... that is you... and pass to the drain which is 'grounded.' It is even worse if you try and grab the hair-dryer to toss it out. If you have the chance, get out of the tub without touching the hair-dryer or anything metal.

Most, if not all, areas of the USA require GFI (Ground Fault Interrupt) outlets in the bathroom and kitchen. Some appliances (such as hair-dryers) may have a GFI style plug already on it. GFI detects if there is any current NOT going through the regular 'neutral' part of the circuit and trips a circuit breaker if there is a fault (such as current going to ground via the bath tub.)

3. If I'm in a bathtub, and drop a battery powered (DC) appliance into it, would I get electrocuted the same as with an AC appliance plugged into the wall?

No. For one thing most battery powered appliances are 12 VDC or less. Also that 12 VDC (or whatever it is) is in relation to the terminals on the battery. It is not in relation to ground (the metal fixtures in your tub.) To get any noticeable shock at all you would need a higher voltage and some part of your body would have to come (electrically) between the terminals on the battery in the appliance. So dropping a non-waterproof flashlight or battery powered drill or whatever in the tub may ruin the flashlight or drill but it won't ruin you.

If you dropped an old fashioned battery powered tube radio (from the 1950s and earlier) which has a 400VDC battery in it then it could get ugly but it is unlikely.

So... dropping a hair dryer in your tub while you are in it is very dangerous. But if someone drops a hair-dryer in the opposite end of a large swimming pool from you it is unlikely you would even notice. If you are climbing out of the pool on the metal ladder and the hair dryer is dropped in to the pool very close to you then there could be problem.
Swimming in a small lake during a thunderstorm is very dangerous. People can swim at one end of, say, Lake Superior and there may be a thunderstorm at the other end with lots of lightning strikes and they are in no danger.

There is no simple rule for calculating the amount of danger in a given situation because it depends on so many factors. Basically it is proportional to how much voltage (and therefore how much current) and how big the 'conductor' (the pool, tub, lake, whatever) is and how much of that conductor is you and how close you are to the source and the ground.

 

[Metal Minister]

Despite popular belief, it is not actually the water than conducts electricity. Rather, it is impurities in the water (such as salts) which are the conductors. Pure water is a terrrible conductor.

I'm not sure about the size of the body of water - probably to due with resistance the further the electricity has to travel.

That's interesting, but from my research, electricity will always seek the path of least resistance. If you drop an a/c powered device into a lake, you are not not the quickest path to ground, and it is dispersed to the point that it is no longer as dangerous. Now LIGHTNING on the other hand....

 

[Michael]

When you plug in, say a lamp with a switch... if the switch is off then the the electrons do not flow anywhere. because the circuit is still 'open.' When you turn the lamp on the circuit is now 'closed' (yes it is a bit counter intuitive) and the electrons will then flow back and forth (AC) through the filament of the lamp.

Other strange thing is that while switching on the lamp is almost instantaneous (practically speaking it IS instantaneous) the electrons themselves do not move very fast. They flow in one direction at about 84 meters/second max in a 12 gage wire carrying 10 Amperes. But they only do this for half a cycle then they flow back at the same speed. Doing some back of envelope math says they will travel about 0.7 meters back and forth. It is unlikely that any given electron in the lamp itself will ever leave the lamp cord if it is 1 meter long.

So... when the cord is not plugged in they go nowhere. When something is plugged in and off, they go nowhere. When something is plugged in and turned on they go a short distance back and forth. In AC circuits thy do not make a 'round trip.' I a DC (direct current) circuit they do make a 'round trip.'



Pure unionized water has much higher resistance than you. Dropping a hair-dryer (that is plugged in) in to the bath tub will connect the current from the wall socket to the water in the bath. The electric current will 'spread out' through all the water AND you, and will take the path of least resistance... that is you... and pass to the drain which is 'grounded.' It is even worse if you try and grab the hair-dryer to toss it out. If you have the chance, get out of the tub without touching the hair-dryer or anything metal.

Most, if not all, areas of the USA require GFI (Ground Fault Interrupt) outlets in the bathroom and kitchen. Some appliances (such as hair-dryers) may have a GFI style plug already on it. GFI detects if there is any current NOT going through the regular 'neutral' part of the circuit and trips a circuit breaker if there is a fault (such as current going to ground via the bath tub.)




No. For one thing most battery powered appliances are 12 VDC or less. Also that 12 VDC (or whatever it is) is in relation to the terminals on the battery. It is not in relation to ground (the metal fixtures in your tub.) To get any noticeable shock at all you would need a higher voltage and some part of your body would have to come (electrically) between the terminals on the battery in the appliance. So dropping a non-waterproof flashlight or battery powered drill or whatever in the tub may ruin the flashlight or drill but it won't ruin you.

If you dropped an old fashioned battery powered tube radio (from the 1950s and earlier) which has a 400VDC battery in it then it could get ugly but it is unlikely.

So... dropping a hair dryer in your tub while you are in it is very dangerous. But if someone drops a hair-dryer in the opposite end of a large swimming pool from you it is unlikely you would even notice. If you are climbing out of the pool on the metal ladder and the hair dryer is dropped in to the pool very close to you then there could be problem.
Swimming in a small lake during a thunderstorm is very dangerous. People can swim at one end of, say, Lake Superior and there may be a thunderstorm at the other end with lots of lightning strikes and they are in no danger.

There is no simple rule for calculating the amount of danger in a given situation because it depends on so many factors. Basically it is proportional to how much voltage (and therefore how much current) and how big the 'conductor' (the pool, tub, lake, whatever) is and how much of that conductor is you and how close you are to the source and the ground.

Wow, what a great explanation.

Welcome to the board by the way.

 

[Dizredux]

I used to use an old photographic density meter which used a 300 volt battery. I wouldn't kill you but you knew it for sure when you were bit.

Dizredux

 

[Old Ned]

Great answers guys.

 

[UnderstandForgive]

1. There are AC outlets in my house. When I plug a cord into them the electrons flow into the cord. Where do the electrons go when the plug is not plugged in? Do they make a round trip back to their source?

2. If I'm in a small amount of water, like a bathtub, and drop an AC powered appliance into it, I'll likely be electrocuted to death. I assume that if I were in a larger amount of water, such as a lake, I wouldn't be. Is there a mathematical formula to express how electricity disperses through water? (I recall that there is some formula to express the dispersion of light.)

3. If I'm in a bathtub, and drop a battery powered (DC) appliance into it, would I get electrocuted the same as with an AC appliance plugged into the wall?

These are excellent questions.

I don't know to well how it works, but I do know a couple things.

electricity travels much better (meaning its able to transfer current over long distance) through copper wire at AC power at 60hz than it does with DC current, I do not know if that is the case with tap water.

I would like to know why it is, when you put a toaster in a bathtub, it electrifies all the water, I would think that it would only electrify the water in the vicinity of the two terminals. (It's hard for me to understand why it is the electrons tend to flow so far away from the terminals of the power source).

For instance if you have a power source (AC or DC) and the + - terminals are just an inch from each other, why don't the electrons travel in a straight line? Why do they have to go all over the bath tub? Would this be the same for less or more conductive materials, does it matter how frequently the current is oscillating? Suppose that the water were a near perfect conductor of electricity, wouldn't that mean that the electrons would be able to take the path of least resistance (shortest distance), So it must have something to do with the resistance of the water. Maybe there is a resistance of the water (say only allows a certain amount of electrons per cubic cm to flow in a given direction) So it needs as much volume to get the electrons to get from point A to B with least resistance.

The way I think of it is. Imagine you have a river, and there is a bolder in it, the water goes around it. Then imagine you add another and another, and the river widens around all these bolders. So the electrons are trying to go from A to B this short distance but there are a bunch of little bolders in the way, causing resistance, so they have to take the long way around, only a certain amount of water can go through the bolders in the straight path of the river, so the more water you add, the more it will fan out. So I imagine the reason (to answer my own question) has to do with resistance. But if you think about that analogy is wrong. Because the Battery terminal is IN THE BATHTUB, so its like having all these bolders and then having to squueze the water back into the narrow river with the bolders in it. It doesn't make sense. There is something else going on here.

Oh I think I figured it out, I read somewhere that Faraday came up with a law that the electromotive Force is equal to negative of the change of magnetic flux creates EMF (Electro Magnetic Force) through a material, meaning that when the magnetic field change changes, it causes electrons to move. using that, I know that an AC current will electrify the water much more uniformally than a DC current because, as the current reverses direction, It generates an electromagnetic force (moving other electrons) perpendicular to the current double derivative of the current (so a sin wave like an AC current would generate a -sin wave perpendicular to that current). (I believe that is the case, my understanding of how electromagnetic force is generated may be wrong. I am basically using the left hand rule and Faraday's observation. And thus generates more electrons to move, double derivative of that current perpendicular and so on and so forth.

 

[Chesterton]

Its kind of like a waterhose, if it isnt used electricity doesnt go anywhere. The controls at power stations can sense that electricity isnt being used as much and then creates less electricity.

Funny comparison, because I also don't understand how water comes into my house without building up too much pressure when not being used.

When you plug in, say a lamp with a switch... if the switch is off then the the electrons do not flow anywhere. because the circuit is still 'open.'

So... when the cord is not plugged in they go nowhere. When something is plugged in and off, they go nowhere.

But they can't just be motionless. They have to be moving somehow, in some direction, don't they?

So... dropping a hair dryer in your tub while you are in it is very dangerous. But if someone drops a hair-dryer in the opposite end of a large swimming pool from you it is unlikely you would even notice. If you are climbing out of the pool on the metal ladder and the hair dryer is dropped in to the pool very close to you then there could be problem.
Swimming in a small lake during a thunderstorm is very dangerous. People can swim at one end of, say, Lake Superior and there may be a thunderstorm at the other end with lots of lightning strikes and they are in no danger.

There is no simple rule for calculating the amount of danger in a given situation because it depends on so many factors. Basically it is proportional to how much voltage (and therefore how much current) and how big the 'conductor' (the pool, tub, lake, whatever) is and how much of that conductor is you and how close you are to the source and the ground.

That makes sense. Thanks.

For instance if you have a power source (AC or DC) and the + - terminals are just an inch from each other, why don't the electrons travel in a straight line? Why do they have to go all over the bath tub?

Good questions too.

 

[Radagast]

1. There are AC outlets in my house. When I plug a cord into them the electrons flow into the cord. Where do the electrons go when the plug is not plugged in? Do they make a round trip back to their source?

The "signal" for electrons to move propagates at the speed of light. The electrons themselves move much more slowly, as Embedded said. Given that it's AC, they reverse direction before they've travelled very far, so actually they just jiggle back and forth.

2. If I'm in a small amount of water, like a bathtub, and drop an AC powered appliance into it, I'll likely be electrocuted to death. I assume that if I were in a larger amount of water, such as a lake, I wouldn't be. Is there a mathematical formula to express how electricity disperses through water? (I recall that there is some formula to express the dispersion of light.)

You may well get electrocuted even in the lake. It depends on what the easiest paths to ground are.

3. If I'm in a bathtub, and drop a battery powered (DC) appliance into it, would I get electrocuted the same as with an AC appliance plugged into the wall?

It will depend on the voltage.

But they can't just be motionless. They have to be moving somehow, in some direction, don't they?

When the electrons are not being "pushed" by an external voltage, they just hang around the atoms they belong to.