Volts, Watts, Amps, and Ohms

Thank you,
Glenn F.

This will come up with many pie chart-type pictures that really make sense. I have one hanging on the wall.

VIRGINIA = RHODE ISLAND

V = RI

John T

E is electrmotive force. Its unit of measurement is the Volt (V). A Volt is defined as the difference in electrical potential across 1-Ohm of resistance when 1-Ampere (i.e. 1-Coulomb/Sec) of Current is flowing.

1-Volt = 1-Amp X 1-Ohm (E=IR)

E is measured in V Volts
I is meaasured in A Amperes
R is measured in (need a Greek letter here) Ohms.
(Yeah, I know there's a key code, but I'm too lazy to look it up - might not work on this forum WP anyway).

Electrical current is the movement of electrons, which are the negative charges of atoms. Obviously they are attracted to a more positive potential. That is, current flows from the more negative terminal of a source of electrmotive force (such as a battery) to the more positive terminal through an external circuit (resistor, lamp, motor etc.). However, inside the source of emf (battery), current effectively flows from positive to negative to complete the entire circuit. In a battery, a chemical reaction produces the electron unbalance between its two terminals that is its emf.

In an electro-mechanical generator, electrons are displaced in a conductor passing through a magnetic field. Unfortunately, magnets have two opposite poles, so a conductor that continues on through a magnetic field will soon have to encounter the opposite magnetic field which will reverse the electron displacement - This produces alternating current (AC) in the conductor (back & forth). The mechanical DC generator uses a clever arraingement of commutator segments and brushes as a switching mechanism to keep the internal coil currents flowing in one direction in the external circuit, although it is a basic AC generator internally. The Automotive-type alternator uses solid-state diodes (one-way conductors) in place of the commutator & brushes to produce DC rather than AC at its output.

It would be difficult to teach a basic electricity course here but volts,amps,watts and ohms all interact See Chart. Just for reference not electrical code which is another subject 120 volts X 20 amps = 2400 watts. That would be 24 100 watt bulbs. Resistance of all the 24 bulbs in parallel would be 120 volts divided be 20 amps for 6 ohms total resistance.

An ampere is the unit of current, which is nothing more than how many electrons pass through a conductor in a particular period of time. To be specific, it is a "coulomb" of charge per second. A coulomb equals 6 x 10¹⁸ electrons. So if you could see electrons and count them very fast, you could measure current. We can make an analogy between current in an electrical circuit and flow in a hydraulic system.

A volt is a measure of electrical potential. Basically if you excite electrons, they acquire electrical potential. In the hydraulic analogy, voltage equals pressure.

The ohm is a little different sort of unit than the amp or volt. Amperes and volts can be defined in terms of more basic units (such as coulombs and seconds), but resistance is simply the ratio between voltage and current in a conductor. So you must be able to measure both voltage and current to determine resistance. In fact, "Ohm's Law" is misnamed. It's not a law at all, at least not in the scientific sense. It would be better to say that "Ohm's Law" is the definition of what an ohm is. By the way, the reciprocal of resistance is conductance. Conductance is measured in "mhos". (Really. I'm not making this up!)

A watt is a unit of power, similar to horsepower. (In fact, 1 horsepower equals about 746 watts.) And power is a rate of doing work, or expending energy. More power means you can do more work in the same time or the same amount of work faster. The watt is defined as one joule of energy per second. If you have one ampere of current applied to a load with a voltage of one volt, that load is receiving 1 watt of power (or one joule of energy per second). Joules are very small units, so we normally use a much larger unit for energy, the kilowatt-hour.

One last thing. Everything I've said so far is true in DC circuits. (At least I think so.) It's also true in purely resistive ac circuits, such as light bulbs and resistive heaters. However, there are reactive ac loads, such as motors, that behave a little differently. Without going into a lot of detail, power to an inductive load does not equal voltage times current. It's actually a little less. So you will see a couple of terms "volt-amps" and "power factor". Volt-amps means just that: voltage times current. Power factor is the ratio between actual power and volt-amps. So if a 100 watt motor has a power factor of 0.7, then it actually needs 100/0.7 = 142 volt-amps.

Ohms law (named after Mr Ohm) tells us where V is Volts, I is Amperes, R is resistance that:

V = RI I = V/R Power in Watts = V x I = I squared x R = E squared/R

Volts namded after Volta I believe is Electro Motive Force or the measure of potential electrical difference between 2 terminals

Amps is a measure of the flow of current through a conductor or medium connected between 2 points having a Voltage difference between them. Its also measured in terms of Coulombs per second which is a measure of the electron flow.

Power in Watts is a product of Volts x Amps

Energy is what the electric utility charges you for and thats a function of power over time i.e. Watt Hours or Kilowatt hours etc. If you burn a 100 watt lamp for 2 hrs you have used

100 watts x 2 hrs = 200 watt hours or 0.2 KWH

Get it????? ?

John T

No, I don't entirely get it. If V=volts, what is the E in your equation "= E squared/R"? Is it also volts, the way Deano used it in the posting immediately prior to yours? Just a typo?

And if E is voltage, then are the formulas stating that power can be computed by multiplying the volts times the amps, or by multiplying the square of the amps times the resistance (in ohms?), or by dividing the square of the voltage in volts by the resistance (in ohms?)

Thanks, Stan

YES Power = V x I or E x I = I squared R = E squared /R = V squared/R

John T Longgggg gg retired electrical engineer

Another area where engineers and non-engineers differ is in the direction that current travels. Non-engineers say current travels from negative to positive. (Military electronics schools are particularly obstinate about this.) But any engineer will tell you that current travels from positive to negative. Why? Because if you don't define current from positive to negative, your calculations will always turn out the negative of what they should be!

Any thoughts????? ?/

John T

Electron current flows negative to positive ( proton is a large mass charged aprticle.. electron is a low mass negatively charged particle... when drawn to each other, the small particle is the one doing most of the moving.. )

Conventional current just the opposite.. positive to negative.. eg hole current theory.

in our electronics classes we always did the math as electron current as that was what was actually happening.. not something made up to make the math come out easier.

Soundguy

I was reading a telephone refference text that stated before the transistor was invented, electrical theory stated electron flow was negitive to positive.

Had the two boys who invented the transistor never reversed this known theory, we would not have electronic componets.

T_Bone

The direction that current flows is just a convention, nothing more. Engineers deal with mathematical models, and it just makes everything work out easier if we pick positive to negative instead of negative to positive. What the electrons are doing doesn't matter to an engineer, he only looks at the math.

Most non-engineering schools want to deal with things on a subatomic level, so the direction that electrons flow becomes important. Now in the vacuum tube days it was hard to gloss over the direction of electron flow, since it was quite obvious that electrons get emitted from the heated cathode. With semiconductors, it's easy enough to just pick one direction since the internals of a transistor are not obvious. Now when semiconductor engineers talk about "holes", it really more of a convention than anything real. Current is still the movement of electrons, and electrons always travel from negative to positive.

Now it may seem like a silly thing to discuss, but the current convention that a person uses has a big effect in their thinking. For example, engineers have a marked bias toward NPN transistors versus PNP. That's because NPN transistors work the "right" way. Many years ago I trained military technicians on a '70s vintage electronics system, which was a mismash of transistors, diodes, integrated circuits and relays. I would take them through the logic paths and they would get very confused. Then I realized that the person who drew up the schematic thought current flows positive to negative, but the techs had always been taught the opposite. I told them to momentarily forget what they'd been taught, and believe that current flows positive to negative. Instantly they caught on: suddenly the schematic made sense.

Amps are a measurement of how many electrons are flowing.

Watts is a measurement of power and is the relationship between amps and volts.

For instance your 100W bulb. The formula is P=I*E, P=watts or power, I=amps or current flow,E= energy or volts. So, a 100W bulb works out as 100W/120V=.833A So your 20A breaker will run 24 for three hours or 19 continuosly because the breakers get derated 20% when enclosed.

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