Liberal Arts Blog — Water Analogies (Hoses and Rivers) and the Knife (Amps) and the Murderer (Volts)
Liberal Arts Blog — Wednesday is the Joy of Science, Engineering, and Technology Day
Today’s Topic — The Mystery of Electricity — Water Analogies (Hoses and Rivers) and the Knife (Amps) and the Murderer (Volts)
Electricity is ubiquitous in modern life, and absolutely indispensable, but it is also hard to understand intuitively. The most common analogies used to explain it are the water hose and the river. But what kills you amperage or voltage? What is the knife? what is the murderer? Who cares? who should? Experts — please chime in. Correct, elaborate, elucidate.
THE WATER HOSE ANALOGY: volts versus amps versus ohms
1. Volts = the water pressure.
2. AMPS = diameter of the hose
3. Ohms = sand in the hose
NB: Your thumb: squeezing the hose with your thumb changes the diameter of the hose (AMPS) which increases the pressure (voltage). A transformer does this by changing the number of coils wrapped around a magnet (more coils, smaller diameter, higher voltage). Transformers only worK with AC power. Batteries use DC power.
THE RIVER ANALOGY
1. Voltage = steepness
2. Amps = volume of flow
3. Conclusion: it’s amperage not voltage that kills you.
THE KNIFE, THE MURDERER, THE RESISTANCE
1. The Amps are the knife.
2. The Voltage is the murderer.
3. And resistance matters.
NB: It is the current traveling through you that kills you but it’s the voltage that makes that current possible and resistance that determines how much current goes through you. Your resistance can vary from 1000 ohms to 100,00 ohms depending on whether you are sweating on a humid day with your feet in bucket of water or not…Under such conditions a mere 50 volts can kill you. On a very dry day with no feet in bucket it could take 5000 volts to do the job. The rule of thumb is that a current of 50 mAmps through you is lethal.
FOOTNOTES — Tesla and Edison, Power versus Energy
1. Tesla (AC power) beat Edison (DC power) in the “war for the grid” but Tesla cars use both DC power (stored in the batteries) which is converted to AC to operate the motor.
2. Power versus energy. Power is a measure of capacity, energy of delivery. Power is measured in kilowatts. Energy in kilowatt hours. You are billed monthly for energy usage.
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