Radio dropped in a lake?
November 5, 2010 7:48 PM   Subscribe

What would happen if you had a radio attached to a power outlet and you like dropped that radio in a lake? Would everyone in the lake die? How would it work?
posted by xmutex to Science & Nature (17 answers total) 3 users marked this as a favorite
Your breaker would switch, assuming you had fairly modern electrical infrastructure.
posted by wayland at 7:51 PM on November 5, 2010

Response by poster: Let's say I didn't. How effective would the electricity be vis-a-vis a lethal force?
posted by xmutex at 7:53 PM on November 5, 2010

It would short out fairly quickly and stop conducting electricity, wouldn't it?
posted by starvingartist at 8:04 PM on November 5, 2010

Consider it this way. Electricity will ground as quickly as it can. If you drop a radio in a bathtub, and you're in the tub, chances are you will be the conduit through which it grounds... If you drop that radio into the ocean, how close would you have to be for YOU to be the conduit through which it grounds...? That lake of yours is someplace between the bathtub and the Ocean... The odds are probably closer to the "Ocean" scenario than the "bathtub" situation... it's all relative....
posted by HuronBob at 8:05 PM on November 5, 2010 [1 favorite]

Even though water (with some salt in solution) is a conductor, it also acts as an resistor. At some distance away from the radio, there's enough resistance that it would act as an insulator, the same as the insulation on a cord, etc. Those in close proximity would likely get a shock, those further away not so much.
posted by mikesch at 8:13 PM on November 5, 2010 [2 favorites]

Since everything (give or take superconductors, and even then…) has some resistance, current takes the shortest/easiest path. This isn't necessarily a direct line though; more like the classical experiment with a magnet & iron filings - you get a field of ever-decreasing intensity the further the path travels, with the size of the field depending on the conductivity (& other factors) of the path material.

In your scenario, there's likely 2 paths - active to neutral (inside the appliance, with a field extending & decreasing outside) and active to earth (from the appliance, through the water, to the nearest 'ground'). If you're within a few inches or directly between the active and ground you'd probably feel a large (& potentially dangerous) shock. Within a few feet you may feel it, but be largely unaffected. Further away, and the effects would be minimal.

Interestingly, around here a few years ago there were calls to ensure that bath drains were grounded to ensure ELCBs worked if you dropped your radio or hair dryer into the bath with you (since modern plastic tubs and pipes meant they were no longer connected to earth via the pipework). It was shown that this could in fact increase fatalities, since it created a path from active -> water -> you -> earth.
posted by Pinback at 8:15 PM on November 5, 2010 [1 favorite]

I have a boathouse on a lake. I was using a power tool plugged into an outlet which is on the same electric bill as the house when I dropped it into the lake. Rather than grab it by the cord and pull it out, I quickly ran to the breaker box to turn off that outlet before I grabbed the drill. In the approximately 4 minutes it took to do all that and return to the lake, the only thing that happened was my drill was fried. Not dead fish, no dead people and nothing appeared to be an issue.

I know nothing about electricity other than I like it a lot; it keeps me in cold food, warm food and light. And my one bonehead moment with it turned out to be just that a bonehead move with no harm done other than the drill. Granted, I am a sample of one, but I would not be concerned if I was in a lake and my neighbor was as big a bonehead as I am. (Turns out she is, but that story is for another day.)
posted by AugustWest at 11:12 PM on November 5, 2010 [1 favorite]

I really doubt that it would be dangerous more than a few feet away from the radio, but if I were betting my life on it, I'd stay a lot further away than that. Pulling a number out of my ass, I'd think 20 feet would be safe, barring really unfortunately placed metal canoes / old sunken wire fencing / whatever.

As Pinback says, the most current will flow near the dropped radio, probably between the two power conductors, but also between the hot wire and the (literal) earth. The first of those will drop off rapidly with distance (dipole, so fourth power). The second, perhaps less rapidly with distance, and less predictably.

There are several distinct mechanisms by which electricity can kill you. I think in this case there are two things to worry about: it could cause your muscles to contract, keeping you from swimming, and you drown; or it could mess with your heart. It takes only a tiny amount of current (a few milliamps) to affect your heart. Fortunately, it's usually hard to get the current to go through your heart. But if your skin's wet, it doesn't offer as much resistance (the difference between dry skin and even slightly sweaty skin is significant). And inside your skin, you're pretty conductive. If your body is more conductive than the lakewater (perhaps if it's a particularly pure mountain lake?) then perhaps you could get some current flowing through you even at a distance from the radio.

The thing about electrocution is, since you can be killed by so little current in the right place, it's really hard to place a solid, safe lower bound. But you can place a "usually won't kill you" bound.
posted by hattifattener at 12:29 AM on November 6, 2010

People do occasionaly die from swimming near boats with damaged electrical systems. The danger is larger in fresh water but it can happen in salt water as well. Some links Fresh water electric shock drowning

I know all marinas in The Netherlands have GFCI's required on the electrical outlets, and all my boats have RCDs wired in the electrical system to prevent this. Not everyone does this, and I would not swim in a marina anyway, especially in fresh water.
posted by atrazine at 12:50 AM on November 6, 2010

Anecdata: I know a person who was pulling a metal canoe out of a lake when lightning struck the lake. I don't know how close the strike hit, but it was close enough that he clearly saw it happen, and it scared him. At the moment of the lightning strike, he was holding the canoe, and he had one leg in the water and one on shore. He said the leg-in-the-lake basically froze stiff for a moment and he couldn't move it at all; he experienced a terrible muscle spasm in that leg which basically charley-horsed him for a few hours and hurt like hell. The rest of his body was unaffected. It was unpleasant, but essentially he was fine. If something as big as lightning at pretty close range does only does that, I'd imagine a radio would do much, much less.
posted by pseudostrabismus at 2:31 AM on November 6, 2010 [1 favorite]

Another anecdote with boat electrics. I recall reading some guy's account of him trying to swim back onboard his friend's boat and nobody realized there was a problem with the electrics. As he approached the boat he started to feel weak and had trouble swimming and couldn't climb the ladder. The slow motion of the boat opened the distance and he recovered, then it happened again as he approached, boat slowly moved away, rinse, repeat. After a few cycles of this, one of the people on the boat clued in that something must be wrong with the electrics and turned them off and the guy was then able to board the boat. Apparently the range at which he began to be affected was only a few feet, so that's probably similar to the effective range of any potential trouble from the scenario you describe.
posted by barc0001 at 2:41 AM on November 6, 2010

if you had a radio attached to a power outlet and you like dropped that radio in a lake

Think of how many lightning storms are going on right now across the planet. How many air-water strikes? And yet I can go walk a couple of blocks and stick my feet in the Atlantic Ocean without getting electrocuted.
posted by Civil_Disobedient at 5:49 AM on November 6, 2010

Everyone in the lake will die. But not from the radio.

The radio you imagine is plugged into the wall outlet. It has TWO wires.. hot and neutral (and sometimes a third called ground.)

In the lake, the hot lead and ground lead will be shorted via the water, and any current flow will be localized to the closest two points where these two wires connect.

Now, is some idiot cut the two wires with a knife, put one in his left hand and one in his right hand, he'd get a shock, and probably lethal.

But your somewhat inadequately described scenario would not injure anyone and would just result in a soggy, broken radio and no tunes.
posted by FauxScot at 7:33 AM on November 6, 2010

The lake IS the ground, electrically. Until the fuse blows, the electricity will dissipate into a sort of cloud around the radio further and further out until there is no more electrical potential. Which is a few feet, I would imagine.

The reason for the boat thing is that our bodies are more conductive than the water and we provide an easier path between "near" and "far" than the water. So we are getting shocked with something less than standard supply power.
posted by gjc at 7:57 AM on November 6, 2010

Something that needs to be kept in mind when comparing lightning strikes with other electrical scenarios - a bolt of lightning is an electrical charge that has developed enough potential to break past the resistance of the open sky. If you think about that for a sec - that is a hell of a lot of power.
posted by randomkeystrike at 8:15 AM on November 6, 2010

Extension cord and powerstrip in a swimming pool. Consensus in comments there is that nothing much will happen.
posted by notyou at 11:43 AM on November 6, 2010

This is basically how electrofishing works. You put a cathode and anode in the water, turn on the generator and create a potential voltage gradient between and around them (a field). When a fish or (person) encounters the gradient the amount of voltage they encounter depends on a) how far apart the cathode and anode (ie the size and shape of the field) b) the size of the fish and where they are in relation to the cathode and anode, ie how much of a voltage gradient they encounter across their body c) if you're using AC or DC d) the amps and e) lots of other stuff like the conductivity of the water, clothing, scales, salinity etc.

In the case of a radio you'd have a huge potential gradient over a very small area. If a large fish/ person encountered that gradient a lot of electricity would move through them. A small or tiny fish or a person wearing waders would probably be totally unaffected. The size of the field would depend on the conductivity of the water but it probably wouldn't be very large because your cathode and anode are so close together. You definitely wouldn't kill everyone in the lake but you might zap the snot out of someone close to the radio and consequently drown them.
posted by fshgrl at 3:04 PM on November 6, 2010

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