Opposite charges attract. Electrons are negatively (-) charged, while protons are positively (+).
Copper has a single electron in the outer layer, which is easily transferable, which makes it a good conductor.
When a battery is introduced to a copper wire, the negatively charged (-) copper electrons start moving towards the positively charged (+) battery node. The negative (-) battery node supplies new electrons, and so they flow i.e. make a current.
The amount of electrons flowing in a given part per second is the current.
In reality, current flows from negative (-) towards positive (+). The convention is to denote it the opposite way i.e. positive charges flow from positive (+) to negative (-). This convention was falsely established by Benjamin Franklin in 1747 due to not knowing electrons exist, and it's too much of a hassle to fix.
Electrons are repelled by the negative terminal of the battery, and are attracted to the positive terminal.
Inside the positive terminal of the battery there is a chemical reaction taking place that "consumes" electrons. The reaction creates an electric force that tugs on the electrons in the attached wire, pulling them into the battery.
Over at the negative terminal of the battery there is a different chemical reaction that sets electrons free. Those electrons don't pile up in the battery, they flow out into the wire. That's how there is a current flowing everywhere in the circuit.
If a rock is put on top of a mountain, it has a potential energy, which is converted into kinetic energy as soon as it starts falling. The rock does work each time it hits an object like trees.
The same with electrons. The battery supplies negatively charged electrons which move towards the positive battery node. The electrons do work each time they hit a component like resistors.
Higher mountain = Higher votage
http://amasci.com/elect/vwatt1_short.html
http://amasci.com/elect/elefaq.html
http://amasci.com/ele-edu.html
http://amasci.com/elect/vwatt1.html
http://amasci.com/miscon/elect.html
Voltage “pushes” charges through an object which has electrical resistance, and this heats up the resistive object. The flow of the charges is measured in amperes, the flow of electrical energy and heat output is measured in watts, and the resistance is measured in ohms.
Electric current isn't stuff, electric current is the flow of stuff. What is the name of the stuff? Charge.
Electronics devices all use DC, while AC is used to bring power to them, which is then rectified into DC via power supply units.
What flows in wires?
- Charges
- Electrons
- "Charge-stuff"
A quantity of charge is measured in units called COULOMBS, and the word "ampere" means the same thing as "coulomb of charge flowing per second." Why do I think amperes are confusing? Well, suppose you had no name for water, yet your teachers wanted you to learn about "fluid flow". Suppose you had to learn about "gallons-per-second," but without knowing anything about water, or about gallons. If you'd never learned the word "gallon", and if you had no idea that water even existed, how could you understand "fluid flow?" That's the problem with electricity and amperes.
You can only understand the flow (the amperes) if you first understand the stuff that flows in wires: the charge, the coulombs.
"Charge" is the stuff inside wires, but usually nobody tells you that ALL METALS are full of charge. Always. A hunk of metal is like a tank full of water, and the "water" is the movable electric charge inside it. In physics classes we call this "the electron sea" or even "electric fluid." This charge is part of all metals. In copper, the electric fluid is the outer electrons of all the copper atoms.
The movable charge-stuff within metals gives them their silvery color. We could even say that charge-stuff is like a silver liquid (at least it is silver when it's in metals.)
Note that this charge is "uncharged", it is neutral. Is this impossible? No. The charge inside of metals is neutral because each electron has a corresponding proton nearby, and the fields from the opposite charges cancel out. The charge is cancelled, but this doesn't mean that the charge-stuff is gone! Even though the charge inside a metal is cancelled out, we can still force it to flow along. We can make the electrons flow past the protons.
When the charge-stuff within metals is forced to flow, electric currents are created. We measure the currents in terms of amperes. The faster the charge-stuff moves, the higher the amperage. Also, the MORE charge-stuff that flows (through a bigger wire) the higher the amperage. A fast flow of charge through a narrow wire can be the same current as a slow flow of charge through a bigger one.
Here's a way to visualize it. Bend a metal rod to form a ring, and weld the ends together. Remember that all metals are full of "liquid" charge. If you push a magnet's pole into this ring, the magnetic forces will cause the electron-stuff within the ring to turn like a wheel (as if the ring contained a movable drive-belt). By moving the magnet, we pump the charges, and the charges flow. That's how electric generators work.
Generators are magnet-driven charge pumps. The moving magnetic fields push the wire's charges, creating the amperes, but this only occurs when a complete circuit is present. Break the ring and you create a blockage, since the charges can't easily jump across the break in the ring. A complete ring is a simple electric circuit. Cut the ring and install a battery in the cut, and the battery can pump the ring's charge-stuff in a circle. Make another cut, install a light bulb, and the "friction" of the narrow filament against the flowing charge-stuff creates high temperatures, and the wire filament inside the bulb glows white-hot.
Important note: the charge-stuff flows extremely slowly through the wires, slower than centimeters per minute. Amperes are an extremely slow, circular flow. See SPEED OF ELECTRICITY for info.
Inside the wires, the "something" moves very, very slowly, almost as slowly as the minute hand on a clock. Electric current is like slowly flowing water inside a hose. Very slow, so perhaps a flow of syrup. Even maple syrup moves too fast, so that's not a good analogy. Electric charges typically flow as slowly as a river of warm putty. And in AC circuits, the moving charges don't move forward at all, instead they sit in one place and vibrate. Energy can only flow rapidly in an electric circuit because metals are already filled with this "putty." If we push on one end of a column of putty, the far end moves almost instantly. Energy flows fast, yet an electric current is a very slow flow.
"Watts" have the same trouble as amperes. They are the name of an electrical flow, but what does the flowing? Energy. A "watt" is just a fancy way of saying "quantity of electrical energy flowing per second." But what is a quantity of energy? Quantities of energy are measured in Joules. A joule of electrical energy can move from place to place along the wires. When you transport one joule through a channel every second, the flow-rate of energy is 1 Joule/Sec, and "one Joule per second" means "one watt."
What is power? The word "power" means "energy flow." It might help you to avoid thinking about "power" at the start. If you first practice thinking in terms of energy flow instead of power, and joules per second instead of watts, eventually you'll gain a good understanding. Once you know what you're talking about, then you can start speaking in shorthand. To use the shorthand, don't say "energy flow", say "power." And say "watts" instead of "joules per second." But if you begin by saying "power" and "watts", you might never really learn what these things are, because you never really learned about energy flow.
OK, what then is electrical energy? It has another name: electromagnetism. Electrical energy is the same stuff as radio waves and light. It is composed of magnetic fields and electrostatic fields. A joule of radio waves is the same as a joule of electrical energy. What does this have to do with understanding electric circuits? Quite a bit! But I'll come back to this later.
How is electric current different than energy flow? Let's take our copper ring again; the one with the battery and the light bulb. The battery injects joules of energy into the ring, and the light bulb takes them out again. Joules of energy flow between the battery and the bulb. They flow at nearly the speed of light, and if we stretch our ring until it's thousands of miles long, the light bulb will still turn off immediately when the battery is removed. Well, not IMMEDIATELY. There will still be some joules moving along the wires, so the bulb will stay on for a tiny fraction of a second, until all the energy arrives. Remove the battery, and the light bulb goes dark ALMOST instantly.
Note that the joules of energy flowed ONE WAY, down BOTH wires. The battery created them, and the light bulb consumed them. This was not a circular flow. The energy went from battery to bulb, and none returned. At the same time, the charge-stuff flowed slowly in a circle within the ring. There you have the difference between amperes and watts. The coulombs flow slowly in a circle, while the joules flow rapidly from an "energy source" to an "energy sink". Amperes are slow and circular, while watts are fast and one-way. Amperes are a flow of copper charges, while watts are a flow of energy created by a battery or generator.
But WHAT ARE JOULES? That's where the electromagnetism comes in. When joules of energy are flying between the battery and the bulb, they are made of fields. The energy is partly made up of magnetic fields surrounding the wires. It is also made from the electric fields which extend between the two wires. The electrical ENERGY flows in the space around the wires, while the electric CURRENT flows inside the wires.
There is a relationship between amperes and watts. They are not totally separate. To understand this, we need to add "voltage". You've probably heard that voltage is like electrical pressure. What's usually not taught is that voltage is part of static electricity. If I grab electrons from a wire, that wire will have excess protons left behind. If I place those electrons into another wire, then my two wires have oppositely imbalanced charge. They have a voltage between them too, and a static-electric field extending across the space between them. THIS FIELD IS THE VOLTAGE. Electrostatic fields are measured in terms of volts/distance, and if you have a field, you always have a voltage. To create voltage, take charges out of one object and stick them in another.
Remember the battery in the copper ring from above? The battery acted as a charge pump. It pulled charge-stuff out of one side of the ring, and pushed it into the other side. This caused a voltage-difference to appear between the two sides of the ring. It also caused an electrostatic field to appear in the space surrounding the ring. And finally, it caused the charge-stuff inside the light bulb filament to begin flowing. In this way the voltage is like pressure. By pushing the charges from one wire to the other, a voltage causes the two wires to become positive and negative. The light bulb provided a path to discharge them again, and this created the flow of charge in the light bulb filament. The battery pushes charge through itself, and this also forces charge to flow through the light bulb filament. But where does energy fit into this? To understand that, we have to know about electrical friction or "resistance" to.
Imagine a pressurized water tank. Connect a narrow hose to it and open the valve. You'll get a certain flow of water because the hose is a certain size and length. Now the interesting part: make the hose twice as long, and the flow of water decreases by exactly two times. Makes sense? If we imagine the hose to have "friction", then by doubling its length, we double its friction. (This happens whether the water is flowing or not.) Now suppose we connect a very thin wire between the ends of a battery. The battery will supply its pumping pressure (its "voltage"), and this will cause the charge-stuff of the thin wire to start moving. Double the length of the wire, and you double the friction. The extra cuts the charge flow (the amperes) in half. THE FRICTION IS THE "OHMS", IT IS THE ELECTRICAL RESISTANCE. To change the charge-flow, we can change the resistance of our pice of wire by changing its length. But we can also change the flow by changing the pressure. Add another battery in series. This gives twice the pressure-difference applied to the wire ends. Which doubles the flow. We've just discovered "Ohm's Law", which says that the flow is directly proportional to the pressure difference, and if the pressure goes up, the flow goes up in proportion. It also ways that if the resistance goes up, the flow goes DOWN by a proportional amount. The harder you push, the faster it flows. The bigger the resistance, the smaller the flow (if the push is kept the same.) That's Ohm's law.
Whew. NOW we can get back to energy flow.
Lets go back to the ring with the battery and bulb. Suppose the battery grabs charge-stuff out of one side of the ring and pushes it into the other. This makes charges flow around the circle, and also sends energy to the light bulb. It takes voltage to force the charges to flow, and the light bulb offers "friction" or resistance to the flow. All these things are related, but how? (Try bicycle wheel analogy.)
Here's the simplest electrical relation: THE HARDER THE PUSH, THE FASTER THE FLOW. This is called "Ohm's Law", and we can write it like this:
VOLTS/OHMS = COULOMBS/SEC
It says that a large voltage causes coulombs of charge to flow faster through the wire. But we usually think of current in terms of amps, not in terms of flowing charge. Here's the common way to write Ohm's law:
VOLTS/OHMS = AMPERES
Voltage divided by resistance equals current. Make the voltage twice as large, then the charges flow faster, and you get twice as much current. Make the voltage less, and the current becomes less.
Ohm's law has another feature too: THE MORE FRICTION YOU HAVE, THE SLOWER THE FLOW. If you keep the voltage the same (in other words, keep using the same battery to power your light bulb), and if you double the resistance, then the charges flow slower, and you get half as much current. Increasing the resistance is easy: just hook more than one light bulb in a series chain. The more light bulbs, the more friction, which means that each bulb glows more dimly. In the bicycle wheel analogy mentioned above, a chain of light bulbs is like several thumbs all rubbing on the same spinning tire.
Here's a third way of looking at Ohm's law: WHEN A CONSTANT CURRENT ENCOUNTERS FRICTION, A VOLTAGE APPEARS. We can rewrite Ohm's law to show this:
AMPERES x OHMS = VOLTS
The more current, the more volts you get. Or, if the current is forced to stay the same and you increase the friction, more volts appear. Since most power supplies provide a constant voltage rather than a constant current, the above equation is used less often. Usually we know the voltage, and we want to find the amperage. However, transistor circuits involve constant currents, so the above ideas are very useful.
But what about watts? When charge is being pushed through an electrical resistance, electrical energy is lost and heat is created. A certain amount of energy is flowing into the resistor device every second. If we increase the voltage, more energy flows into the resistor and gets converted to heat. If we increase the flow of charge, same thing: more heat flows out per second. Here's how to write this:
VOLTS x COULOMBS/SECOND = JOULES/SECOND
For every coulomb of charge that's driven through the resistor, a certain number of joules of electrical energy flow into the resistor and they flow out as heat.
The charge flow and the energy flow are usually written as amps and watts. This conceals the fact that quantities of "stuff" are flowing. But once you understand what's really going on inside a circuit, it's simpler to write amperes of charge flow and watts of energy flow. IF WE INCREASE THE VOLTAGE, THE CHARGE FLOW INCREASES, AND THE ENERGY FLOW INCREASES EVEN MORE. Doubling the voltage-pressure caus
VOLTS x AMPERES = WATTS
We can get the Ohms into the act too. Just combine this equation with Ohm's law. If you increase the voltage, it increases the flow of charge through the electrical friction device. But since voltage AND current both get larger at the same time, the energy flow increases even more. If voltage doubles, current doubles, and wattage doesn't just double, instead the doubling doubles too (wattage goes up by four.) Write it like this:
VOLTS x VOLTS / OHMS = WATTS
So, if you double the voltage, energy flow increases by four, but if you double the friction while keeping voltage the same, energy flow gets cut in half (not in 1/4.) The amperes change too, but they're hidden. Here's one final equation. It's the same as the one above, but voltage is hidden rather than ampereage:
AMPERES x AMPERES x OHMS = WATTS
So, the watts of energy flow will go up by four if you double the current. But if somehow you can force the current to stay the same, then when you double the friction the energy flow will double (and the voltage will change.)
Volts - Difference in electric potential i.e. desire to go back to equilibrium charge. “Pressure (Water pump)”
Ohms - Resistance (Pipe narrowing) No resistance = Short Circuit.
Coulombs - Charge (Positive Protons, Negative Electrons) a bag of electrons.
Amperes - Current (Rate of charge (matter) flow) Number of charges flowing per second.
Joules - Energy
Watts - Power (Rate of energy flow)
Separated charge = Static
Combined charge = Matter
Analogy:
AIR is a physical substance. SOUND is a wave that propagates rapidly through a volume of air. WIND is a flowing motion of air already present.
ELECTRIC CHARGES are a physical substance. ELECTRIC ENERGY is a wave that travels via a column of charge. ELECTRIC CURRENT is a flowing motion of the charge already present.
Anything above 10 mA (0.01A) can produce a painful to severe shock and is the “let go threshold”. Currents between 100 mA (0.1A) and 200 mA (0.2A) are lethal due to ventricular fibrillation. Interestingly, higher currents than 200 mA are not lethal per se, but will render a person unconscious by stopping his heart (complete clamping due to muscle contraction), as well as burn the body. The person has a good survival chance if CPR is performed immediately.
However, without sufficient voltage, amps are irrelevant. The combination of both is lethal. At 100V, 50% of the population had a skin resistance of 1,800 Ohms, which would result in 55 mA, which is rather dangerous and potentially lethal. For the same resistance, 18V would be the point after which pain starts.
Force (Newtons) x Distance (Meters) = Work (Newtons Meters)
Joules are also units of Work, however they are used as a unit of Energy. Work uses the same units as Energy because Work is just a change in Energy.
Energy = The ability to do work.
There are many types of Energy, in this case we talk about Kinetic Energy (Motion) and Potential Energy (To be used Energy).
Potential Energy = Energy that could be used to do work. (Gravitational, Spring)
Energy can neither be created nor destroyed.
Power = Work / Time i.e. Watt = Joules / Second
Static electricity occurs when an object obtains a net amount of positive or negative electric charge, creating an imbalance that wants to be returned to equilibrium.
An atom has a net charge of 0 because of the positive protons and negative neutrons cancelling each other.
In solid materials, protons stay fixed while some electrons are free to move around when acted upon by an outside force. This ability to move around varies between materials, with some being conductors and others insulators.
What makes them move? It’s the imbalance of electrical charge i.e. when one part of an object has a different amount of free electrons vs another.
Negative charge = Too many electrons. Positive charge = Missing electrons.
If a charged object is connected to a much larger neutral conducting object, the net charge gets redistributed to the large object i.e. the small object loses its net charge. When that large object is the Earth, this is called grounding i.e. allowing net charges to leak into the ground, rendering the smaller object neutral.
Coulomb’s law calculates the force (attract/repel) between small particles.
When we have an object with a known net charge, can we predict how other net charges will react when they pass nearby?
Michael Faraday hypothesized that every charged object generates an electric field that permeates space and exerts a force on all charged particles it encounters.
An electric field is a measurable effect generated by any charged object.
The field carries energy and passes it on to other charged materials by exerting electric forces.
Mindfuck Crash Course video.
Voltage = Difference in electric potential.
Resistors cause a voltage drop. Batteries cause a voltage rise (give the charges energy), which is why the voltage is 0 at the negative battery end, in order to go up to the battery’s voltage.
According to the conservation of energy aka Kirchoff's Voltage Law, the total voltage supplied to the system is equal to the sum of all the voltage drops across the circuit i.e. The sum of the voltages in a loop (that is, the sum of how the potential energy changes along a path that comes back to its original point) must equal zero (Second Law). Also, all the current flowing to a splitting junction must be equal to the joining junction (First Law).
For every branch in a parallel connection, the voltage is the same, no matter the resistance. If a river flows downhill and splits into two branches, with one being severely blocked and the other partially… Where will most of the water flow? It’s the same with current i.e. flow of charge will follow the least resistance.
A capacitor in a DC circuit is useful for storing charge temporarily and releasing it again later.
The amount of energy per unit of charge. 1 Volt means that every coulomb of charge is "carrying" 1 joule of energy.
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I don't really know anyone who actually thinks about voltage in J/C terms unless doing some calculation and using unit analysis to check their answer. Voltage is the driving force behind current. You could describe voltage as the desire of the charge to move across a potential difference. But I feel that it is important to include the phrase "across a potential difference" just saying "from here to there" makes it seem like it is a property of the object itself, when voltage is a property of the electric field. Placing a charged particle inside a large potential difference is going to make it reallllly want to get down to a lower potential. Particles do not like being in high energy states. So when you connect a circuit they're going to see a path that they can take that will allow to to reach that lower energy state. This is the reason it takes work to bring a charge into a field. The charge doesn't want to be there. It is interacting with the field itself and receiving a force. In a universe with zero electrical potential all charged particles would be infinitely far from each other.
The reason the concept is important for capacitors is that in a capacitor the energy is actually stored in the field itself. They don't go into depth about why this is the case, because truthfully for a PHY II course it's not really that important. Once you start talking about the properties of fields and why they do what they do, you start delving into very completed quantum dynamics.
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What is voltage, really? Voltage is very much a convenient way to keep track of electric potential energy. As you know, voltage is in terms of energy per charge. So that means that if a positive charge goes from somewhere with lower voltage to somewhere with higher voltage, it is gaining potential energy. To make an analogy, you can kind of think of voltage like altitude. If you know something gained altitude, then it gained gravitational potential energy.
This analogy with altitude also helps describe how the movement of charges is affected by voltage. Charges will want to move from an area with high energy to low energy, similar to how balls will want to roll or slide downhill. For positive charges, this means they will want to flow from high voltage to low voltage, while the opposite is true for negative charges.
Voltage, like energy, is relative. Whenever you talk about voltage, you are referring to the voltage at one point compared to the voltage at another point. For example, a common battery is 1.5 volts. This means that the positive terminal is 1.5 volts higher than the negative terminal. Equivalently, you can say that the negative terminal is -1.5 V when compared with the positive terminal.
Batteries are a pretty useful thing to visualize voltage with. If you complete a circuit with a battery, charges start to flow from one end to another. You know that the charges exiting one end of the battery start with some potential energy (i.e. starts with some voltage), but loses all of it by the time it re-enters the battery. Since that potential energy is missing, it must have gone somewhere, such as being lost as heat, or perhaps driving a motor. Since you know how many joules per coulomb were lost from one end of the battery to the other, in order to find the total energy lost, all you need to know is the total amount of charge (Coulombs) that were driven by your battery.
As for capacitors, putting a voltage across the capacitor ends means you're putting an energy difference from one plate to another. Again, this means that if you complete a circuit, charges will want to flow from the high energy side to the low energy side. Therefore, a capacitor is a way to store electrical potential energy.
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"Electric potential" is literally just the potential energy a positive charge of +1 would have at that point. So forget the electron for now, does it make sense? When located at the positive end, a positive charge has a lot of potential energy because it is going to get pushed away towards the negative charges at the other end. Now we can remember the electron, and just reverse everything. Since electric potential is based on positive charges, and a positive charge would have high potential energy on the left side of the picture, an electron will be opposite. It makes sense; if it is negatively charged, it's perfectly happy to chill out next to those positive charges.
Another way to think of it is by analogy to gravity. We can say height is electric potential, and things with mass are positive charges. So if you are at the top of a cliff, you have high electric potential and high potential energy. The thing that makes electric fields difficult is that to put negative charges into this analogy we would need to imagine that there is some other type of object made of anti-gravity material, and that the top of that cliff is really the top of all existence. The anti-gravity stuff will chill at the top of the cliff, so it actually has low potential energy up there...but when you bring it down to the bottom, it wants to fall back up. Ok. So this makes some sense. BUT--if we are "reversing everything" as you say, then I still don't understand why a particle that is happy and otherwise doesn't want to leave would have a high potential in an area where it has low potential energy. High potential to do what? It doesn't want to go anywhere.
That's why it's confusing that they have such similar terms. For a positive charge, electric potential and potential energy are basically the same thing. For a negative charge, being in an area that has low electric potential (near negative charges) will give it high potential energy because it "wants" to get over towards the positive charges.
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Electric Potential Energy works very similarly to gravitational potential energy. If you lift a stone off the ground, you do work to lift it, and in the process, you give it gravitational potential energy. The same thing happens with charges. If you move a charge a distance from another charge, you do work to move it and you give it electrical potential energy. In either one, when you release the stone/charge they will move back together.
The problem with the analogy though is that for gravitational potential energy, you need another mass, in this case the earth to create the gravitational field you are interacting with. In electrical potential energy, you don't actually need a charge in the other location. You could just have an electric field created by a changing magnetic field or something. We don't have any other way to create gravitational fields so having something like gravitational potential just isn't useful for anything.
Electric potential gives us a way to describe energy in a field without depending on the charges involved. You can pick any two points in the field, and find the Electric Potential between them without knowing anything at all about the charges. This is useful, because there may not actually be any charged objects involved. Then, if we do actually want to know something about energy, say we drop a charge in there, then simple multiplication can tell us how much energy it has.
This is particularly handy in an electric circuit where we have a source of electric potential like a battery. With a battery with an electric potential of 12 Volts, we automatically know that every 1 Coulomb of charge that goes from one side of the battery to the other will be able to do 12 Joules of work. If I need 120 Joules of work to be done, then I either need to make sure 10 Coulombs of charge can go through the circuit, or I need a bigger battery so I can get by with less charge. By knowing the electric potential of the battery is 12 Volts I can easily figure out all sorts of other things without needing to know how many charges are in the battery.
The total amount of charge passing through a wire over a period of time.
When there is a difference in electric potential between two points, the voltage gives charged particles like electrons the energy to move from one place to another. Just like a river flows from high elevation to low, electric charge flows from high voltage to low voltage.
*While water pressure and flow are a handy way to mentally model electrical voltage and current, it is worth noting that electrons themselves move very slowly (only millimeters per second) through a conductor in the direction opposite the current ("electron drift speed"), while electrical current moves close to the speed of light. The way to picture this is, that the electrical conductor is a tube, packed full of balls from one end to the other. When you push a ball (electron) in one end of the tube, it almost instantly forces a ball out the other end of the tube. The speed at which that pressure information is transmitted from one end of the tube to the other is the speed of electrical current, while the speed at which the balls move through the tube is electron drift speed.*
To extend the water analogy, voltage is like pressure while current is flow rate. One way to model it is like this. Picture you have a dam with a full reservoir of water behind it. If you poke a hole in the dam near the top, it has very little pressure behind it, which is equivalent of low voltage. The water flows through the hole relatively slowly. Poke same sized hole in the dam near the bottom and it has great pressure behind it, so the water shoots through the hole in a fast moving stream. The size of the hole represents resistance where smaller hole = greater resistance. Given I = V/R, can see that if voltage is increased while resistance remains same, flow rate increases. Similarly if resistance is made smaller (hole is made larger) then flow rate increases.
When you push 100 electrons (or 100 quadrillion) in one end of the wire, that causes an electrical field (due to voltage pressure) that propagates through the conductor almost instantly pushing a different 100 electrons out the other end of the wire. The average velocity of the electrons themselves known as the "electron drift velocity" is extremely slow and for a normal D/C battery powered circuit is only millimeters per hour.For an A/C circuit the net drift velocity is zero and the electrons simply oscillate back and forth within the conductor. The conductor does in fact store a vast quantity of electrons (10e29 per m^3 in metal) at net zero position, until an electrical field is applied (voltage pressure), and then electrons are added at one end of conductor, and others forced out the other end. The simplest analogy for how this works is that the conductor is like a hollow pipe full of balls. When you push a ball in one end, it forces a different ball out the other end as fast as that pressure can be communicated. For highly conductive metals the pressure can be transmitted closed to the speed of light. In less conductive materials as low as half the speed of light. But the velocity of the balls themselves is relatively slow except at the kind of voltage pressures you'd use in a super collider (Gigavolts).
Resistance prevents current from flowing. If there's zero resistance, as in some kinds of short circuits, the current will flow in the wire without any losses. The basic rule is Ohm's Law:
V=IRV=IR
If VV is non-zero, and RR is zero, then the current II will be infinite.
This means that if you just connect the two leads of a battery together, current will flow, draining the battery as fast as the underlying chemistry can generate charge. That happens even with a plain old ordinary conductor: the resistance is low, and the current, while not infinite, gets really, really high. This is pretty dangerous, since the battery wasn't designed to handle being shorted out. It can cause chemical leaks or even catch on fire.
So for any actual DC circuit, there had better be something somewhere in the circuit providing resistance. Some circuits, like ones with just an LED, will have a resistor put in there just to limit the current. The LED will take as much current as you want to give it, so a current-limiting resistor is added to keep it from trying to drain the battery in a flash (perhaps burning itself out in the process).
In a series, the current is the same for all resistors and the voltage drop changes. The total resistance is R1 + R2
In a parallel, the voltage is the same for all resistors and the current through each changes. The total resistance is 1/R = 1/R1 + 1/R2.
The equivalent resistance for a parallel setup of resistors will actually be smaller than any one of the resistors in the circuit i.e. the two river branches join eventually no matter their separate resistance, resulting in a greater flow.
All the outlets in your home are connected in parallel. No matter how many devices are connected, they all get the same voltage.
Once we know the total resistance and the voltage, we can derive the total current in the system with Ohm’s law. V = I x R or I = V/R.
Once we know the total current, we can find the voltage drops across every single resistor. The voltage drop can be calculated again with V = I x R. If we have 20V and one resistor with 10 Ohms and another with 5 Ohms, with a current of 1.3A, the voltage drop in the first resistor would be 10 x 1.3 = 13V, which would mean that the voltage drop is now 20V - 13V = 7V for the next resistor and the rest of the circuit.
Attaching a voltmeter (Huge resistance) in parallel with a resistor will measure the voltage for it, since it’s the same in parallel. In series, it will show nothing because the resistance is very large in a voltmeter i.e. it breaks the circuit.
Attaching an ammeter (Zero resistance) in parallel will blow it up because all the current will now run through it with no resistance. Attaching it in series will measure the amps, but the circuit must be broken beforehand, otherwise it would short it.
Inductors prevent the current from starting or stopping immediately by delaying it i.e. gradually increasing or decreasing it over time.
Power (Watts) = Voltage x Current
If the voltage is low, a lot of power is lost as heat (>80%) while traveling over long distances. The equation states that for the same power, lower voltage translates to higher current and power loss increases proportionally to the square of the current. In other words, if the voltage is doubled, there is only ¼ of the power loss. Tripling the voltage is 1/9 of the power loss etc. The increase in voltage is done with transformers which only work with AC.
AC alternates because of the way it’s produced in generators, i.e. by rapidly switching the polarity of magnetic fields i.e. by rotating a wire loop inside a uniform magnetic field. The rotating speed is usually 60 Hz which means AC changes direction 60 times per second.
Electronics devices all use DC, while AC is used to bring power to them, which is then rectified into DC via power supply units.
Three phase power is ideal for applications that require heavy loads. Also, it’s used to transfer 3 times the power with the same grid.
Three phases = 3 equal live wires going into a building, where the alternations in current are out of synch by ⅓, hence 3 phases. This way, more power can be drawn without risking an imbalance.
Only the particles in SOLID METAL flow from negative to positive. The rest can be bi-directional (batteries, human body, sky, ocean…)
Electric currents produce three main effects: magnetism, heating, and the voltage drop across resistive conductors. These three effects cover almost everything we encounter in electronics. And these three effects don't care about the amounts of positive and negative particles, or about their speed, their mass, their charge, etc. If a hundred positive particles flow to the left per second, this gives exactly as much magnetism, heating, and voltage as a hundred negative particles flowing to the right per second. We don't care about the real polarity of the particles. We don't care about their speed, and we don't care about their number. We ignore both the chemical effects and the effects of the velocity and direction of moving particles. We ignore the collisions between positive and negative particles. All we care about is the total net charge which moves past a particular point in the circuit. The real charges are too complicated to deal with, and the added complexity gets us very little information as long as we're only interested in voltage drop, magnetic fields, and heating. Once we start ignoring the speed and direction of the charges, then we can easily build electrical instruments or "amp meters" which measure the Conventional Electric Current in terms of the magnetism which the charge-flow creates... or by the voltage drop which appears across a resistor, or by the temperature rise being created in a calibrated piece of resistance wire. For more than 99% of electricity and electronics, the direction of the particles is irrelevant, and an ammeter tells us the so-called "real" current while hiding the true particle flows. Or to put it simply: we pretend that "electric currents" are always composed of POSITIVE particles of unknown speed, so that any negative currents are defined as positive particles flowing backwards rather than negative particles flowing forwards.
"Electricity" is not made of electrons (or to be more specific, Electric Charge, which is sometimes called "Quantity of Electricity," is not made of electrons.) Charge actually comes in two varieties: positive particles and negative. In the everyday world of electronics, these particles are the electrons and protons supplied by atoms in conductors. Electrons and protons carry electric charges of equal strength. If electrons are "electricity", then protons are "electricity" too.
Now everyone will rightly tell me that the protons within wires cannot flow, while the electrons can. Yes, this is true... but only true for metals. And it's only true for solid metals. All metals are composed of positively charged atoms immersed in a sea of movable electrons. When an electric current is created within a solid copper wire, the "electron sea" moves forward, but the protons within the positive atoms of copper do not.
Electrical energy belongs in the electromagnetic spectrum. Electrical energy is electromagnetic field/wave energy.
High current is fast charges. Zero current is stopped charges.
Students end up thinking that the Amp is a fundamental unit; they ignore the Coulomb-per-second, and are confused by the Amp-second. The situation should be reversed: they should learn all about the Coulomb, hear about current only in terms of Coulombs per second, and should see the Amp-second as a strange, roundabout way of saying "coulombs."
It's impossible to grasp because of the wide use of a confusing phrase "amount of current." No, current is actually a rate, not a substance-like quantity. Instead we should be careful to say it this way: "what's the rate of current," or "intensity of current", or "what is the value of current."
It's impossible to grasp because early textbooks wrongly mix the concept "quantity of a substance" with concept of "flow rate of a substance." This mistake occurs not only in electricity. Does a shower use lots of water? Meaningless question, since the length of time is not given. Or, is a high current actually a flow of "lots of electricity?" Meaningless, since it's the amount electricity flowing per second, not just electricity flow. Is a 1000W lightbulb a user of "lots of energy?" Meaningless. A 1000W bulb uses energy at a greater rate than a smaller bulb. If I turn on a small bulb for a year, versus a large bulb for a microsecond, the small bulb uses way more energy.
A battery is not a supplier of "current electricity," it instead supplies voltage, and various currents are drawn by placing various resistances between the battery leads.
Power is NOT a substance-like entity which can flow. Power is actually a flow of a substance. "Power" means energy-current. Energy can flow, and its rate of flow is called power.
Electric energy is NOT made of small particles called electrons. Actually, the fundamental unit of electrical energy is the photon, not the electron, since electrical energy is electromagnetic field/wave energy.
Energy DOES NOT flow up one wire, through the appliance, then back down the other wire. Energy actually flows up both wires, dives into the appliance, and is converted to other types of energy (heat, motion, etc.)
Electric companies DON’T sell electrons. They actually sell 60Hz "radio waves", and only use the columns of electrons in the wires to transmit the waves to the end users.
Energy DOESN’T flows inside of wires. Electrical energy is actually electromagnetic fields. It exists as the voltage field and magnetic field which surround the wires. Electrical energy flows as a "tube" which encloses a pair of wires and exists only outside the metal.
individual electrons in wires DON’T carry energy along with them as they flow. The situation is really like that with sound: the energy moves as waves through a population of particles.
We shouldn't teach about "current" until after we've taught the "electron sea" concept. It's like learning about ocean currents without ever learning that water exists. It makes "current" seem needlessly abstract and non-visualizeable.
Instead of saying that conductors allow current, and insulators prevent it, say that conductors contain mobile charges, while insulators contain immobile charges.
electric current is NOT a flow of energy, it is actually a flow of matter.
electrons flow like the minute hand on a clock, and if they were to flow fast enough that you could see a movement, that wire would be heated white hot by "friction." The electric fluid acts like tar: it stops instantly when the pressure is removed, gets hot from friction when forced to move, never moves very fast, large flows require huge pipes, small pipes are subject to very high friction, and fast movement always implies immense heating.
Wires are not empty pipes waiting for water to flow. Wires actually behave like pipes full of water, with no bubbles anywhere, so when more water is pushed into one end, water immediately flows from the far end.
Electric circuits are like pulley/belt systems, the electron-sea within a metal wire is like the rubber belt. When one part is moved, the whole thing turns, when one spot on the belt is clamped, the whole thing stops, no rubber or electrons are consumed, the belt moves slow in a circle while the energy moves fast in waves, the belt is not invisible and neither are the charges, back-and-forth motion sometimes works better than continuous rotation (AC vs DC), friction causes heat and even light, pulleys can drive or be driven (motor/generator duality), pulleys are not a source of rubber and batteries are not a source of electrons, and when the belt or the circuit is stopped, the rubber or electrons stop in place and forever remain. And belt-systems were in actual use until supplanted with generators and wires.
A "charged" battery contains just as many electrons as a "discharged" battery, because batteries store their energy as chemical fuel, a battery is simply a chemically-fueled electron pump, and is "charged" with chemical fuel, not with electrical energy. A fully charged battery contains the same net electric charge as a discharged battery. (yet it contains huge amounts of matter, which is made of charge!)
Misuse of the word "charge": when a battery is suddenly connected to a pair of long wires leading to a distant lightbulb, the wires become charged and a wave of net charge propagates along the wires at the speed of light. Yet the individual electrons, the "sea of charge," flow slowly around the circuit. So did the charge go fast or slow? Depends on whether "charge" means the electron sea, or whether it means the imbalance in quantities between the group of electrons and the group of protons in the wire. A "charged" capacitor contains exactly as many electrons as an "uncharged" one. Charge imbalance is called "charge", but electrons and protons are also called "charge."
Net charge is an imbalance between pos. and neg. charged particles, and only the negative particles moved. Net charge is the difference between quantities of positive and negative particles, and the net charge can move differently than particles.
"electricity" DOESN’T involves only electrons. For example, mistaken belief that conductors contain movable electrons. This is true only of metals, and is not true of water, human flesh, sparks, neon signs, batteries, currents in the earth,
...mistaken belief that electrons in conductors must be forcibly pulled from individual atoms before an electric current can commence. The "jumping electrons" misconception.
Grounding gets rid of excess charge by leaking it into earth. Without this, all electric devices would explode when lightning strikes, or when a static discharge occurs after a large enough charge imbalance occurs. Electrical outlets have three wires: Hot, Neutral and Ground. The word "ground" means:
- A 'common' connection, but not connected to Earth.
- A direct connection to the power supply (usually to the DC negative terminal.)
- A point on a circuit used as a zero-voltage reference for measuring potential differences.
- A connection to the inside of a shielded metal box.
- A connection to a metal object much larger than the circuit (e.g. car chassis.)
- A connection to a metal stake driven into the earth (or a connection to a metal water pipe which extends out of the house into dirt.)
Only number six is actually connected to ground!