0
\$\begingroup\$

I have a very basic way of understanding things. Sometimes I over-complicate and sometimes i make it way too simple so I am hoping someone can help me judge my understanding of basic electricity. I am in school to be an Aircraft Mechanic and am working part time at an aircraft repair station where I do some Avionics installations.

In school I have learned that

  • Ohms = resistance (opposition of current to flow is how I understand this )
  • Watts = Electrical Power ( What is powering the system )
  • Voltage = Electrical Pressure ( In my head this is what controls the rate that current flows through the system attempting to return to ground )
  • Amperes = Current (This is the flow of electricity through the system but I am a little fuzzy on this compared to voltage because to me they seem like the same thing.
\$\endgroup\$
  • \$\begingroup\$ Using your analogy, "Air" is the same as electrical charge. While current is the analogon of the amount of air flowing from an outlet in a second, pressure is the force which drives that flow. E.g. you double the pressure and the flow per second doubles (roughly). Or you widen the nozzle at the same pressure and the flow per second doubles also. (Let there be a huge air reservoir, so the pressure wouldn't weaken because of a single nozzle.) \$\endgroup\$ – Janka Dec 29 '16 at 3:25
  • 1
    \$\begingroup\$ Possible duplicate of What does a resistor do? \$\endgroup\$ – Ignacio Vazquez-Abrams Dec 29 '16 at 3:26
  • 1
    \$\begingroup\$ Current does not "attempt to return to Ground". In most circuits, "Ground" is just a label we put on a point in a circuit to indicate that we will consider that point as "Zero Volts", and measure voltage in the circuit relative to that point. \$\endgroup\$ – Peter Bennett Dec 29 '16 at 3:41
  • 2
    \$\begingroup\$ @hypfco: In many (most) electronics, the term "Ground" does not imply a connection to the earth - it is just a name we apply to a point in the circuit we want to call "Zero volts". In the OP's case, his aircraft electronics will have no connection to the earth - their "Ground" will probably be the aircraft frame. \$\endgroup\$ – Peter Bennett Dec 29 '16 at 4:47
  • 1
    \$\begingroup\$ @hypfco -- you're dead wrong, sorry. Electricity always attempts to return to where it came from. \$\endgroup\$ – ThreePhaseEel Dec 29 '16 at 23:50
4
\$\begingroup\$

Some find it easier to understand electronics using physical world metaphors:

  • Consider the voltage source as a water pump which produces pounds per square inch of pressure.
  • Consider the wires as pipes.
  • Consider a resistor as a constriction in the pipe.

At every point between the high pressure side of the water pump and the constriction, the pressure is so many pounds per square inch. After the constriction the water pressure drops to zero and the water is free to flow back to the water pump.

Note: Even though all the pressure drops across the restriction, the water still flows!

So, in this metaphor:

  1. The water pressure is the voltage (V).
  2. The water flow is the current (I).
  3. The constriction in the pipe is the resistance (R).

A useful relationship between these is:

V = I x R

...to solve for values other than V just rearrange the equation to suit your needs:

I = V / R

R = V / I

For more on using a Hydraulic Analogy see this Wikipedia.org article.

\$\endgroup\$
  • \$\begingroup\$ I used an answer similar to this in a different question since closed. But the answer (slightly changed) fits this question better. \$\endgroup\$ – st2000 Dec 29 '16 at 4:58
  • \$\begingroup\$ Consider adding this very useful article in your answer: en.m.wikipedia.org/wiki/Hydraulic_analogy \$\endgroup\$ – Brethlosze Dec 29 '16 at 4:59
  • \$\begingroup\$ More precisely, the resistance is the fluid viscosity along with the pipe diameter. The fluid looses energy by heat, just like in a resistor. \$\endgroup\$ – PDuarte Jan 14 '18 at 12:53
0
\$\begingroup\$

Note that you're using the old scientific definition of "electricity," and this can become very confusing if you also read today's books. Old books say that the flow of electricity is called electric current. New books ignore this, change the definition, and insist that "electricity" is the flowing motion itself! (It's like becoming confused about the difference between air and wind.)

Rather than choosing one definition or the other, perhaps it's best to just give up and stop saying "electricity," ever. Pretend that there's no such thing as Electricity. Instead say "charge" if you mean charge, and "current" if you mean charge-flow.

On the other hand, combining the old and new meanings of "electricity" will screw everything up. Here is the result below. Simple and obvious right? Hah!

  • "Electricity" is the movement of electricity.
  • Whenever electricity starts moving, we call the resulting motion by the name "...electricity!"

See? Messed up.

Oh, also you're using the phrase "current flow." That causes problems too. OK, whenever you turn on a faucet, does water come out? Or, does current come out? In rivers, does "current" flow along? Can you fill a bucket with current? Nope. Current means "water flow," and the flow itself does not flow. (Similarly, we can't have a tank full of compressed wind!) In electric circuits, charges can flow inside the conductors. But currents? They never flow, they just appear and vanish as the flow starts up or halts. Things become much clearer if we avoid the word "current," and instead say "charge flow." (Beware, many textbooks will constantly talk about "flows of current," when they should be explaining flows of charge.)

Try this:

  • Ohms = a type of electrical friction. But also an "electrical leakage path" between two wires.
  • Watts = the flow-rate of electrical energy, where watt means "joules per second." (Watts are a rate, not a 'stuff.')
  • Voltage = something like pressure, but more like "altitude." To make water flow downhill, first we need a hill. Voltage is "electric altitude." Two different voltages give us an "electric slope" which forces the charges to move.
  • Amperes = the flow-rate of the charges; the charges which always exist inside all conductors. (Fast charges are high current, slow charges are low current. At zero current, the charges halt, and they remain sitting inside the conductors.)

In school I have learned that

That's a problem, because the low-level books have wrong explanations, and the high-level books use math instead of words. If you're still in school, then you'll get bad grades whenever you give correct answers, since your textbook disagrees. Better to just give the teachers what they want, escape from class, then go off and figure out the correct explanations on your own. Like this:

  • all conductors are already full of movable charges. In metals, these charges are the electrons of the metal, orbiting among all the atoms constantly.
  • Hook a bunch of conductors in a circle. This gives you a loop made of movable charges, almost like a "drive belt."
  • Batteries are charge-pumps. They're always on, always trying to pump, but the air has no movable charges, not like metals do. A battery is a stalled pump, and uses no energy when stalled.
  • If you hook a battery into your circle, the pump starts pumping, and the entire "invisible belt" will start moving like a single object. Charges are moving through the battery. The battery doesn't supply the stuff that flows along.
  • Resistors are like friction. If you hook a resistor in your loop, then the battery will speed up the circle of charge, while the resistor will slow it back down again. The metals' charges circulate, the resistor gets hot, and the chemical fuel inside the battery gets consumed.
  • Break the circle. The break acts like a blockage. Charges can't get past the gap in the metal. The charge-flow halts, and a voltage appears across the break.
\$\endgroup\$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.