My last post on the subject.
Clive,
I think you are a little of the mark here. Perhaps you are confusing a
different type of conductors, tap water is a conductor primarily because it
has impurities which make it an electrolyte, anyway some comments below.
(Comments in the interests of stopping anyone chasing red herrings with
electrical faults)
Malcolm Bagley
Stafford, UK
1975 FJ45 Pickup (In Work)
_______________________________
Actually you could do the above - the water would act like a large value
resistor and the reading would be there, infact you would get a higher
voltage ie less drop the closer you put the meter probe to where the wire
entered the bowl.
Also if you run a bare wire through water the electricity will not stop
flowing - try it with a 6V battery and a bulb.
Table below shows conductivity and resisivity values for water and copper.
Resisivity is the inverse of conductivity.
Conductivity Resisitivity
siemens per metre ohm meter
Tap water 0.05 20
Sea water 5 0.2
Copper 60,000,000 0.00000001666
Unfortunately calculations are more complex (ie use complex numbers) for AC
circuits but imagining Russia uses DC at 230V and the razor blade & water
boiling example;
Resisitivity of tap water (20 ohm meter) multiplied by distance between the
blades in meters (0.025) divided by the area of the blades (0.04m * 0.02m 0.0008) gives a resistance of 625 ohm
P (Power in Watts) = V^2/R
At 230V DC then P = 230 * 230 / 625 = 85 Watts
That seems a bit of a slow boil so the blades might need be closer together,
and Russian water probably had more impurities which make it more
conductive. With sea water the equation gives about 8500 Watts ie 8.5 KW!
(So for a quick cuppa add salt)
Now you see why Reno and Julian both mentioned salty or sea water - also why
people who live near the coast and have petrol cars are careful about
driving through sea water.
I know of someone who drove through the puddles from the spray on the sea
front without a problem, but the next morning the engine wouldn't start, he
left the car, got the bus to college, tried the car when he got home and
found it started, next morning it wouldn't start again. In the end his dad
looked at it and worked out that the salt had dried on the engine and leads
but was combining with condensation being in the mornings, during the day
the engine would dry out and be OK in the afternoon, until the next day.
Malcolm
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