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Carl Fredrik Ahl

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Posts posted by Carl Fredrik Ahl

  1. 3 hours ago, Strange said:

    Holes act as positive charge carriers in semiconductors. 

    Yeah I forgot that, I wrongly though of it as protons, thx for reminding me. 

     

    3 hours ago, Strange said:

    static charges are not affected by a magnetic field.

    Why is this?

    It's quated from this source: https://www.electronics-tutorials.ws/electromagnetism/hall-effect.html

  2. passing a continuous current through itself. When the device is placed within a magnetic field, the magnetic flux lines exert a force on the semiconductor material which deflects the charge carriers, electrons and holes, to either side of the semiconductor slab. 

     

    I wonder why the semiconductor needs to send a current through itself in order for the protons and electrons (positive and negative charges) to get effected by the magnet and get to either side of the semiconductor. There are only negative charge in the current of course (cause it's all electrons, which should result in the electrons getting to one of the sides of the semiconductor, but how does it works with the protons (the positive charges)?

    mag26.gif

  3. 17 hours ago, Sensei said:

    Take a look at the simplest analog voltmeter. It contains resistor with known resistance, very high value like 1 Mega Ohm. Wire goes through electromagnet. There is also solid magnet. When current is flowing through wire, electromagnet is turned on, and repels from solid magnet. The larger current, the more powerful electromagnet, thus needle is repelled more on the scale.

    Ohm's law is I=U/R, so U=I*R. R is constant 1 MOhm. So U is proportional to I.

    The difference between analog voltmeter and analog ammeter is just in this additional resistor. If you switch to ammeter mode, resistor is bypassed.

     

    No, it's not. E=Q * U, so U=E/Q. Voltage is electric potential energy (in Joules) divided by charge (in Coulombs).

    Thx for the answer, but I wanted to know how digital voltmeters works.

    8 hours ago, mathematic said:

    This is not quantum theory - should be in classical physics.

    Ok, can I change that?

  4. I wonder why the speed-cup in this case will follow the magnet: 

    Since they're electric currents, and they're moving in an electrical conductor inside a magnetic field, another law of electromagnetism says they will create motion. How? The currents actually make the speed-cup rotate in such a way that it tries to catch up with the spinning magnet. 

    Source: https://www.explainthatstuff.com/how-speedometer-works.html

  5. 6 hours ago, dimreepr said:

    the engine turns fuel into motion, in reverse, the motion is the fuel

     

     

    Yeah I know this, but I wonder if you know an animation or video where they are engine braking so that I can see directly how it works without trying to imagine the process.

  6. 21 hours ago, koti said:

    Like Dimreepr said, its the other way around.

    Basically, the transmission has a certain resistance which causes the car to slow down when you downshift. There are many gears connected to each other in the car’s transmission, when power is applied there is a certain loss of power due to the transmission resistance. That  loss of power due to resistance is the main factor which slows your car down when you downshift (there are other smaller factors, this is the main one) A good example would be a rally car or race car transmission which is very rigid and has a very high resistance to withstand high power. If you downshift in a car with a transmission like that, you essentially feel like you would hit the brakes really hard. 

    Thx for the answer. Do you know an animation or video showing this?

  7. 4 hours ago, koti said:

    Essentially what happens is you go down a gear in your car, your revs go up (your feet start pedaling faster) but the engine causes a lot more loss of energy due to resistance

    Thx for the answer. Why is the resistance higher when the rpm gets higher and how does it slow down the car. Can you explain in more detail plz.

  8. 3 hours ago, swansont said:

    If the photons are not in phase, they will destructively interfere (to an extent that depends on the phase difference). You can't concentrate light that doesn't exist.

    What do you mean with they interfere? What happens?

  9. On 12/11/2018 at 3:16 PM, swansont said:

    The transition induced is coherent, so the photons are the same phase. That's not happening in fire, or in any other incoherent source. Being monochromatic makes certain optics easier, and the laser is a gain medium, so there is amplification.

    The intensity and the divergence of the beam are not really connected.

    There's only one transition emitting light in a typical laser. Not true of fire.

    Thx for the answer. Does the photons need to be in the same phase in order for the laser to be concentrated? Or is there other advantages?

  10. Hi,

    I know that laser works by giving atoms in crystals or glasses energy so that they can get excited and then jump back to their steady place and that emitts a photon. I also know that these photos only are one wavelength. What I wonder is how they make the lasers so intense so they can reach very long distances and stay concentrated. What makes laser differ so much from fire? Because the color of fire is also photons emitted from the exciting atoms when they jump back.

  11. 7 hours ago, StringJunky said:

    Yes, it detects the magnetic variation as the camshaft rotates. It exploits the Hall Effect.

    Ok, so both the camshaft and a piece of the camshaft sensor is magnetic and when there is a blank spot, the magnetic force between the camshaft and the camshaft sensor decreases and the sensor sends that to the car computer so it will know the position of the camshaft?

  12. On 11/30/2018 at 6:38 PM, Strange said:

    Typically, you measure the time it takes to charge the capacitor or the frequency of a resonant circuit containing the capacitor.

    Can you explain this in more detail please? I don't understand how the capacitor get charged. I understand everything else.

  13. 1 hour ago, Strange said:

    Not sure what your question as the explanation in the video seems quite clear: when the device is rotated, the Coriolis force causes the vibrating system to deform which moves the two capacitor plates and changes the capacitance.

    There is a more detailed description here (of a slightly different structure) which includes videos showing animations of the change in the movement of the vibrating part when it is rotated: https://www.siliconsensing.com/technology/mems-gyroscopes/

    Thx! I meant how the capacitor gets the different charges depending on how far away the masses are.

  14. 19 hours ago, DrP said:

    When a metal is heated the atoms vibrate faster.  This faster vibration can impede the smooth flow of the electrons free to flow through it. (afaik).

     

    Just looked it up:  https://www.quora.com/Why-does-the-resistance-of-a-conductor-increase-with-an-increase-in-temperature

     

    Although the electrons move faster...  so do the molecular vibrations, causing more collisions with the electrons...  so kinda like I said.  There is probably a more detailed explanation somewhere, but that's all I got for now. :) 

     

     

    Thx for the answer!

  15. 2 minutes ago, MigL said:

    The quick answer is that normally the engine 'drives' the wheels, but in your case, the wheels are driving the engine, and effectively doing work by compressing air in the cylinders ( along with gearing, friction, heat, and other losses ).

    Thx for the answer, can you plz explain in more detail how this works, maybe using an illustration.

  16. Hi,

    I know that when your car roll down a hill and you switch to a lower gear, the engine will break and the car slows down. I have heard that it slows down because higher rev in the motor and therefore there will be higher friction. I don't understand how this works, can you please explain?

  17. 15 minutes ago, swansont said:

    Not in a simple oxidation. You just form the new molecule, and the electrons are shared. You need to have a setup where there is a current, and where you can measure it.

    Can you explain in more detail how this works please?

     

    16 minutes ago, swansont said:

    Use a search engine. This information exists already.

    Ok.

  18. 10 minutes ago, swansont said:

    You need to generate a current.

    There is a photodetector that has an output signal (voltage or current) that you measure. If it goes down, it's because there is CO2 absorbing the light, and the amount of the dip is proportional to the CO2 concentration. The values are calibrated at some point with known CO2 sources.

    How does the other components generate the current? Doesn't the oxygen generate current while taking electrons from the lead?

    Can you please show an image or paint one where it's showed how the photodetector operates?

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