Comments by "George Reynolds" (@karhukivi) on "The Engineering Mindset" channel.

  1. Hole flow is what happens in semiconductors, as well as electron flow in the opposite direction. However, in metals there is only electron flow and in electrolytes there is also negative and positive ion flow.
    14
  2. You are forgetting internal resistance which is not zero!
    4
  3. At last, someone with common sense! It doesn't matter which system you use as long as you don't mix them up and make stupid mistakes in circuit design.
    4
  4. A dead battery has a high internal resistance even though the terminal voltage on open circuit stays at 12V. To test a battery you have to load it i.e. draw a significant current from it. You need a new battery, most likely.
    3
  5. The inductance of the relay coil produces a "back EMF" when it is switched off. The energy stored in the magnetic field of the coil appears as a voltage in the opposite direction and the flyback diode just shorts this to prevent it doing something unwanted elsewhere in the circuit which operates the relay.
    3
  6. As a physicist working with electronic equipment for over 40 years I can say it doesn't matter which one you use as long as you understand what you are doing!
    3
  7. Agree. It has to be in conductive ground like wet clay and not dry gravel. A ground test with a Megger is advisable.
    3
  8.  @StoneShards  The electron is like an ant, the charge to mass ratio is huge, so a slow movement of electrons - and there are a lot of them in 1 square millimeter - is plenty to give rise to a large current. They do not travel at 96% of the speed of light, that might be beta particles in air, but not electrons in a metal conductor. The velocity as you say, is proportional to the voltage gradient.
    2
  9. The internal resistance has increased. If you draw almost nil current, the voltage is 1.5, but once a current is drawn through an external resistance, you have to include the internal resistance too.
    2
  10.  @anonymous_FoX The unit mA is current, mAh is capacity. You can short out a 24V truck battery with a spanner and get several hundred amps for a few seconds until the spanner melts! If the battery is not charged enough, or already defective, then it will be discharged if the spanner is left there long enough. By Ohms Law, the resistance is R=V/I so 24/200 = 0.12 Ohms. The starter motor will also draw a current of 100 to 300 Amps. You don't need inductors, capacitors or transistors to get a current of 200Amps. What happens in practice is the resistance will heat up (I^R effec) and the resistance will increase, so the current reduces. If the excess heat builds up, the resistor will melt and/or fail, just like that spanner.
    2
  11.  @therbertme  That is of no consequence in dealing with electricity or electronic circuits. In metallic conductors, the outermost electrons can leave the vicinity of their atom and wander freely through the metallic molecular lattice. In a single atom, these outermost electrons are held, albeit weakly, but when a lot of atoms are present as in a metal, the forces holding them are reduced collectively and they become free to move. These are known as "conduction" electrons and give rise to electricity.
    2
  12.  @millomweb  Alpha particles are charged atoms of helium, they most certainly do exist!
    2
  13.  @captainprototype187  I'm presuming you are talking about a lead-acid (i.e. car-type) batttery or a lead gel-cell? A 12V car headlight (55W) connected to the battery should light for 3 minutes without going dim, and the voltage should still read 12V. If the light goes dim and the voltage drops below 10V then it is the battery that is failing. If this test is OK, then perhaps there is a fault elsewhere in the scooter. Garages also have testers which put a heavy load (100A) to mimic a starter motor load, and that shows up a battery fault immediately. Good luck!
    2
  14. It also bounces higher when dropped onto a hard surface, as the internal components have dried out and become solid.
    2
  15. A flat battery can be recharged fully, a defective battery won't charge properly if at all.
    2
  16.  @WTF_BBQ  "Hole" flow is for semiconductors, not conventional flow as in metallic conductors. Some beginners find a current flowing from negative to positive very counter-intuitive. Also the rules about induction like Lenz's law have to be reversed for electron flow as they were devised for conventional flow. The best thing is to stick to whichever system you were taught for electronics. In physics we always use electron flow.
    2
  17.  @amramjose  Whatever works best for you, stick to it!
    2
  18. Yes, for parallel connection each diode should have its own resistor, not one resistor for all!
    2
  19. Ohm's Law really only applies to metals and direct current and is not really a "law" as there are many things that do not obey it. For example, semi-conductors, ionised gases, ionic solutions, soil and rocks, and incandescent lamps. Alternating current circuits do not obey it if there are inductive or resistive components. Even metals do not obey it at high current densities. However, for most DC electrical circuits it is a fairly useful formula.
    2
  20. A typical LED is lighting normally at 20mA for for a 5V supply, the limiting resistor is found by dividing 5000 mV by 20 mA giving 250 ohms. So a 270 ohm resistor will do just fine. Using a lower resistance the LED might be too bright and even burn out, a higher resistor gives a dimmer light.
    2
  21.  @StoneShards  Yes, "current" as a wave travels fast, but not the electrons! Those executive desk toys with a line of steel balls illustrates that nicely - one ball strikes one end and the ball at the far end jumps off. The wave moved fast but the intervening balls hardly moved at all.
    2
  22.  @StoneShards  Hi Peter, I re-read your message and I see where the confusion arises. The impulse effect of a current is almost instantaneous as you say, but wave motion is not particle motion as you can see in the sea where a wave passes but a floating object just bobs up and down. If you google on "drift velocity" there is a calculation on a Wikipedia page that shows a velocity of 23um/s for a 1A current in a 2mm diameter copper conductor. My estimate was for 10A and would give 83cm/hour for the same 2mm wire, close to my "back of the envelope" 1 metre/hour.
    2
  23. Electrons move through the wire in response to an electric field caused by a potential difference. In the case of DC the drift velocity is about 2-10 cm/hour.
    1
  24. There is no "used" current and no energy levels of electrons involved. Better to think of potentials, the neutral is connected to ground so it has the same potential as "ground" and no current should flow through anyone touching the neutral conductor. The "hot" wire is alternating between +310V to -310V, with an average ("RMS" or "root mean square") voltage of +220V or -220V relative to ground (European system). So if you are standing on the ground (with poor insulation) and touch the hot wire, you will have an alternating current pass through you as the voltage swings up to +310V and then to -310V 50 times per second. Sometimes the neutral is badly connected to earth at the transformer, or the ground is resistive and not at zero potential, or even incorrect wire colours, so touching the neutral conductor is never recommended unless the circuit is turned off, i.e. isolated.
    1
  25. You are correct, the two lamps might not have identical resistances so may not glow equally bright.
    1
  26.  @StoneShards  That was 1 metre per hour, not 1 mile per hour!
    1
  27. You will be on a delicate edge. A shade less voltage and the LED goes out, a shade more and it pops! Not a good strategy....
    1
  28.  @Willy_Tepes  That's correct, to get the ideal current in each LED. Some LEDs have resistors built-in and others are even more clever with current regulation etc. But for plain vanilla LEDs you aim to get the ideal current as per the specs.
    1
  29. Three things could happen - they won't light up, they light up, or one blows. The circuit should be designed for them to light up at a suitable brightness, i.e. the ideal current..
    1
  30.  @franciscoperna7963  It's the current you have to start with. A simple LED (not in some device with other components) will tolerate 10 to 30 mA, (0.01-0.03A) so you must choose a resistor to put in series with the LED that will limit the current. If you want to connect it to a 12V supply, then 12/0.02 = 600 Ohms, so you could use a higher resistor value of 680 Ohm resistor and the current would not exceed 20 mA. There is a small voltage drop across a LED (depending on its colour ; 1.8V for red to 3.3V for blue) so a more exact calculation would be for a blue LED of (12-3.3) 8.7/0.02 = 435 Ohms and nearest resistor value of 470 Ohms for the series resistor. If the LED is not bright enough, you can reduce this resistance to a lower value but if it is too bright, then you risk burning it out. Trial and error is the last resort, I have burnt out many LEDs from experimenting! Hope this helps.
    1
  31. But not equally. More current through the lower impedance path.
    1
  32. It comes from a charge separation between the earth surface and the cloud, and within the cloud also. So lightning can flash between parts of the cloud or from cloud to the ground.
    1
  33. The "preferred" path is the one with the lowest impedance.
    1
  34. Not if they are set into concrete. A metal bar in contact with damp soil is the best.
    1
  35. Because the ground may not be very conductive everywhere. The bar could be in dry gravel while a copper pipe might be in contact with wet soil, so bonding them together prevents a difference in potential between them.
    1
  36.  @augustaking8  You make this sound like religion!
    1
  37. It doesn't "know", there is a potential difference and the current will flow across it if it can.
    1
  38. And some have plastic in places where you don't see it. No guarantee that the "ground" is actually in contact with the earth!
    1
  39.  @augustaking8  You should ask the students doing electricity and electronics that have such difficulty with that. You're clearly not in the teaching profession!
    1
  40. An amplifier is not converting DC to AC, that is an inverter.
    1
  41. That is correct, the outer electrons are the valence electrons and in a metallic molecule, the neighbouring atoms cause the threshold to be lowered and these electrons are then free to move around and become conduction electrons. They do hold energy in discrete amounts in the quantum mechanical domain.
    1
  42. InpPhysics you use electron flow for gases and also for electrochemistry. However for practical electronic design of circuits it makes no difference whatsoever and as the symbols for diodes and transistors have the arrows by convention, and most people can relate to positive "flowing" to negative, it seems slightly more intuitive. We can blame Benjamin Franklin for calling it wrong 150 years before the electron was discovered!
    1
  43. Actually a battery is more like a pump as it is a chemical reaction that is forcing electrons to move. A capacitor is more like a water tank as it is storing charge.
    1
  44. Agree!
    1
  45. Most electronic technicians have used conventional current all their lives with absolutely no problem. Electron current, on the other hand, creates much confusion with a counter-intuitive flow from negative to positive giving some people real difficulties!
    1
  46.  @stevemorse5052  Some devices cannot source much current, so in effect the limit resistor is inside the device connected to the LED.
    1
  47. And a dim LED....
    1
  48. The silver and gold stripes are the tolerance, so they should be on the right and you read the other stripes from left to right.
    1
  49. Yes it is. Most people think "cells" are in prisons or perhaps something to do with cellular phone networks.
    1
  50. Because most of the energy is in the visible band so we see it as light. Normal diodes emit energy in the infra-red band which is perceived as heat. LEDs do produce some heat too, but less than a similar "normal" diode. It is the current which produces the heat, a normal diode might be rated up to 2amps or even more, but LEDs function with a small current of 10 to 50 milli-amps.
    1