Understanding electricity

Discussion in 'Physics' started by wildflower, Jun 18, 2016.

  1. wildflower

    Thread Starter New Member

    Oct 4, 2015
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    I'm trying to understand electricity and would like to avoid using analogies like water since I find they more than often obfuscate the facts and can cause unnecessary confusion.
    I'm not trying to reinvent the wheel or rewrite the textbooks, I'm just trying to explain electricity to myself, and if I'm wrong, please let me know.

    Particles can be either negative (minus) or positive (plus) charged
    Particles with opposite charge attract each other
    Particles with same charge repel each other
    Electrons have a negative charge

    Rearranging the core of an atom (protons and neutrons) require a lot of energy, but electrons can travel fairly easy between atoms.

    Depending on the atoms electron-configuration, it can be more or less conductive.

    Electricity is electrons moving from minus to plus, but as a leftover from old days, most use the conventional way that describes electricity as moving from plus to minus.

    A battery is basically two isolated containers containing positive charge in one end and negative in the other. The negatively charged electrons will be drawn towards the positive side and not forced from the negative side.


    Volt(V)
    How many electrons are available (potential)

    Amp(A)
    Amount of electrons flowing through a connection over time
    1 coulomb = (6.242e18 electrons) pr. second = 1 Amp * 1 sec.

    Watt(W)
    How many electrons are needed to complete work with respect to time. 1 Watt = joule per second

    AmpHour(Ah) = volume/consumption
    How many electrons move in an hour. (Amps x hours)
    1 Ah = 1 Amp flowing for one hour

    WattHour(Wh) = Power consumption. Watt * Hours = Watt Hours

    Joule(J) = 1 joule is The amount of electricity required to light a 1 watt LED for 1 s
    1 Wh represents 3600 joules (3600sec. = 1hour)


    Resistor = resist current flow

    Capacitor = resist change in voltage, can store electrical energy temporarily in an electric field.

    Coil = resist change in current, can store electrical energy temporarily in an magnetic field.

    Diode = only lets current flow in one direction

    Transistor = basically an input-controlled diode
     
  2. MrChips

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    Oct 2, 2009
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    You are mostly correct. Some of your statements need clarification:

    Electrical conductivity is determined by how many electrons are free to move, called free or Fermi electrons. These electrons have energy levels near the Fermi level and therefore have a higher chance of being free to move.

    Electricity is the flow of charge, which can be positively or negatively charged. Electricity in metals is primarily a result of electrons which are negatively charge. There are cases where the charge is positive. If you remind yourself that electrons are negatively charged then conventional current flow from positive to negative potential remains consistent.

    A battery is much more complicated than that. A battery involves an electro-chemical reaction which incorporates movement of both positively charged and negatively charged ions. Because of a table known as the electro-chemical series positive ions will migrate towards the electrode higher in the series while negative ions migrate to the electrode lower in the series. When this happens an electric field is produced in the battery electrolyte which opposes further migration. When this electrical potential is disturbed by creating an external path between the two electrodes more ions will migrate to maintain the proper potential balance. Note that a battery cannot generate electricity in perpetuity. Eventually all of the chemistry is consumed (i.e. becomes neutralized) and your battery goes dead.

    I will leave the definition of electrical units for someone else to answer.


    No. A transistor is much more complex than that. There are two very different types of transistors, 1) bipolar junction transistor (BJT) and 2) field effect transistor (FET) and they operate on very different principles.

    The mechanics of a BJT relies on understanding the nature of electron-hole pairs, how they are created, how they can recombine and how the concentration of electron-hole pairs can be controlled in different regions of a semiconductor device. It goes much beyond the simple understanding of electron flow in conductors
     
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  3. MrChips

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    One other point worth mentioning is that the speed of electrons is extremely low, less than 1 mm/s. When we think of current flow, electrons or otherwise around a circuit, electrons don't actually whiz around the wire. So you are not going to see the electron move from one terminal of the battery to the other.

    Imagine a hollow circular tube tightly filled with marbles. (Sorry, I have to resort to analogies in order to give you the picture). The marbles don't actually make it around the circular tube. What happens is when one marble is made to move all the other marbles have to move at the same time. That is, the information to move travels at the speed of light (or close to the speed of light, i.e. about 60 to 80% the speed of light).
    What we observe as electric current is this information flow while the actual electrons hardly budged.
     
  4. wildflower

    Thread Starter New Member

    Oct 4, 2015
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    Thanks for your reply.
    I understand that these things are a bit more complicated, I'd just like to understand the basic ideas behind, so please excuse my ignorance
    :)

    I thought that all electrons had the same charge, and don't understand how they can have different energy levels?

    I understand that batteries lose power, my knowledge of ions are somewhat limited thou, so I have a bit of reading to do.
    But as I understand it, the end result is that electrons travel from one end to the other, and that the loss is due to electrons being dissipated when they are transformed to other kinds of energy like heat, magnetic and so on?
     
  5. wildflower

    Thread Starter New Member

    Oct 4, 2015
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    The marble analogue is one of the few that actually makes sense to me, and I know that I perhaps oversimplify things a bit too much.
     
  6. MrChips

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    It is difficult to fully understand the nature of electrons without delving into an explanation of quantum mechanics (QM). But we'll try our best without QM.

    Electrons have a fixed charge.

    The energy of the electron can be almost any value.

    We can look at the Bohr model of the atom. Think of electrons as residing in holes or spaces around the atom. We give each hole an energy level or sometimes known as a shell. Each shell has a different energy level. An electron occupying that hole or shell has to have a certain amount of energy. Some holes are occupied while others are vacant. For an electron to move from one hole to another vacant hole it must have the right amount of energy.

    (When electrons move from a higher energy level to a lower energy level, the difference in energy must be given up somehow. If the energy level is the right amount we might be able to observe it as visible light. That is how light emitting diodes (LED) work. Note that the colour of the light emitted by the LED is a function of this difference in energy level. Red light has lower energy than blue light. That is why it was easier to make red LEDs. Blue LEDs took a bit longer to create and only recently a Nobel prize in physics was awarded to professors Isamu Akasaki, Hiroshi Amano and Shuji Nakamura who made the first blue LEDs in the early 1990s. )

    Electrons in the innermost shell are tightly bound to the atom.

    Atoms with electrons in their outermost shell have electrons that are loosely bound. These are the metals. If we give these electrons some extra energy they can break loose from being bound to the atom and we call them free electrons or Fermi electrons. These are the electrons that create electricity in metals.

    When an electric gradient (or potential difference) is applied across a conductive material this electrical field causes the electrons to move ever so slightly producing an observable current.
     
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  7. nsaspook

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    Aug 27, 2009
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    No electrons are dissipated. The battery/wires are already full of electricity. Lets use a bicycle-wheel analogy instead of water. Don't take this too far while trying to understand electricity.:eek:

    Pedals: Battery
    Wheel: Bulb/resistor
    Chain links: Electric charges
    Human: Chemical energy in the battery

    One person turns the pedals to send energy to the wheel while another person has their hand on the rear rubber tire. The electric charges don't dissipate, get lost or get used up but the wheel receives energy (transported through as tension in the bicycle chain) instantly from the pedals as the links move slowly while making the other persons hand hot until the poor person moving the pedal gets tired and stops like a discharged battery. Even if you just move the pedals only up and down instead continuously in one direction the hand gets hot as would be the case in an AC circuit.

    [​IMG]
     
    Last edited: Jun 19, 2016
  8. wildflower

    Thread Starter New Member

    Oct 4, 2015
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    This is absolutely fascinating stuff. My biggest problem with trying to understand electricity, is that everything leads to a new subject that it equally fascinating, and something that I know next to nothing about :)

    So if I understand you correctly, the electrons energy is in relation to the atom it is orbiting, so when it leaves the atom, the energy is zero? or is the energy more like the speed of an orbit, and leaving the atom it would contain it's energy until it either enters another atom or collide with an other particle?
     
  9. wildflower

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    Oct 4, 2015
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    o_O
    I must be getting tired, cause I simply can't wrap my brain around this.

    I better get some sleep and hope my head is a bit more responsive in the morning.
     
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  10. nsaspook

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    Last edited: Jun 18, 2016
  11. nsaspook

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    Good idea as electrical energy flow is not intuitive. It requires a bit of work to think about the somewhat indirect method of energy transfer by charge.
     
  12. KeepItSimpleStupid

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    Mar 4, 2014
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    Totally true.

    Anyway electrons have a "certain" probability to be found in a particular pattern. Each of these patterns have specific energy levels associated with them. It gets pretty intense: https://en.wikipedia.org/wiki/Energy-dispersive_X-ray_spectroscopy When they get knocked from one energy level to another, they emit an X-ray.
     
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  13. wildflower

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    Oct 4, 2015
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    It might be because English is my second language, because after 8 hours of sleep and several wiki-pages, I still can't understand the relation between charge and energy, or rather the difference between the two.

    charge = volts, and energy = ... amps?

    If an electrons energy level is relative to the atom it occupy, how can it transfer energy? doesn't it loose its charge when leaving the atom?

    btw. thanks to all of you for taking the time to help me understand this.
     
  14. MrChips

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    For an ESL person (English as a second language) your English excels that of a lot of folks with English as their native tongue. I have never heard an ESL person use the word "obfuscate". In fact, there is only one member on AAC that would use that word in a post.

    Don't confuse charge and energy. Charge is a fundamental physical constant and the units are coulombs.

    (Off Topic: there is the anti-matter particle, opposite to the electron, called the positron which carries a positive charge. The electron cannot lose its charge unless it annihilates with a positron. )

    Energy of the electron relates to the mass and velocity of the electron and the familiar Einstein equation E = mc^2

    The kinetic energy Ke of an electron moving with velocity v is:

     K_e = (\gamma - 1) m_ec^2


    The effects of special relativity are based on a quantity known as the Lorentz factor, defined as

     \gamma = \frac{1}{\sqrt{1 - \frac{v^2}{c^2}}}

    where v is the speed of the particle.

    https://en.wikipedia.org/wiki/Electron
     
    Last edited: Jun 19, 2016
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  15. wildflower

    Thread Starter New Member

    Oct 4, 2015
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    Thank you, I think I understand most of it now.

    One of the points of my confusion was believing that the electron lost energy moving from the inner ring to an outer ring, but it seams that it behaves the opposite way and produces a photon when moving inwards (using the Bohr model), so leaving the atom it actually have more energy. In other words, the energy level required in the outer ring is greater than the inner ring? and loose electrons have more energy than electrons in the outer ring?

    Math is not my strong side, and calculating the Lorentz factor is a bit complicated, but it seams that v (relative velocity) is the only variable?
     
  16. nsaspook

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    I know it seems like something is missing and it is, we're all dancing about the pink elephant in the room called 'fields'.

    In the bike chain analogy tension (tension describes the pulling force) transfers energy.
    Tension is a somewhat archaic term in electricity for the electric difference of Potential between two points of a Electrical circuit.In this analogy tension (voltage V) together with the motion of the links (current I) form the basis for electrical power (V * I) a time-based quantity of work-energy.

    A very important concept to understand is that free charges (electrons in wires) in conductors have very little energy under normal circuit conditions and the energy they do carry is usually wasted in the circuit so we normally try to reduce that waste by limiting even the tiny bit of energy in the wires unless we want a heater.
    https://www.st-andrews.ac.uk/~www_pa/Scots_Guide/audio/part6/page2.html
     
    Last edited: Jun 19, 2016
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  17. MrChips

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    As one delves more into the mysteries of quantum physics one encounters fascinating phenomena related to electronics.One such example is quantum mechanical tunneling which led to the creation of the tunnel diode.

    The energy level of electrons in the atom is quantized. An electron residing in a given shell has a given energy. In classical theory it is impossible for that electron to cross an energy barrier that is of higher energy. In quantum theory, the energy of the electron is based on probability and there is a small but finite probability that the electron's energy will be higher than the imposed energy barrier. Hence there is a small but finite probability that the electron will "tunnel" through this barrier and find itself at a higher energy.

    This phenomenon arises from the particle-wave duality of the electron. We may think of the electron as a ball bouncing off a wall barrier. With the concept of a wave, quantum tunneling predicts that there times when the wave is able to penetrate the wall.
     
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  18. MrChips

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    Don't let math scare you. Math is a language and you have already demonstrated excellent ability to learn another language.
    Math is the language of physics. Electricity and electronics are fields of physics. Without math we would not be able to solve problems in physics, electricity or electronics.

    Following a comment made in another thread, what would opera be without music? (The answer, of course, would be mime).
     
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  19. nsaspook

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    A very useful tool when used with others to isolate problems.
    5e6e542e792745fe.png
     
  20. crutschow

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    Mar 14, 2008
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    I think all this talk about electron orbits and energy levels is confusing since it has little to do with the transfer of energy by an electric current. As nsaspook noted it's the applied voltage (tension) the determines the energy that is transferred by the current.

    In a good conductor there are electrons from the outer orbit of the atoms that are free to move (how they became free is not important to this discussion but requires a knowledge of quantum physics if you are interested)
    Think of the conductor as being full of electrons that can freely move under the slightest voltage.
    When a voltage is applied across the conductor the electrons move in response to the voltage and are limited by any resistance in the circuit as determined by Ohm's law, I = V/R.
    All the applied voltage is dropped across the resistance, dissipating power in the resistance, P = I*V.

    In a water analogy (bare with me), when the water molecules (electrons) under pressure (voltage) pass by a faucet restriction (resistance) all the pressure (voltage) is dropped and the energy of pressure times water flow (voltage * current) is dissipated at the restriction (resistance).
     
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