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Science HL physics

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  • 24-05-2014 11:56am
    #1
    Kelly090
    Registered Users Posts: 80 ✭✭


    For science I find the electronics chapters in physics really confusing. I just cant get my head around it. Hopefully someone can answer my questions.... How do you know which is the positive and which is the negative terminal of a battery if they do not give the plus and minus signs in the diagram? What does the positive to positive of a diode mean? How do.you know if a diode is in forward bias? Please someone help!


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    #2
    5uspect
    Moderators, Arts Moderators Posts: 10,518 Mod ✭✭✭✭5uspect


    This is the battery symbol for a single cell or a multicell battery:
    fig25.gif
    Just remember that the long line is positive. Typically you put the positive terminal at the top.

    If you're having trouble figuring out circuits, like this one:
    voltage-divider-circuit-ex.png


    Try to recast it like this ignoing the battery:
    00107.png

    The top rail is your positive voltage while the bottom is the ground. Think as voltage like pressure in a network of water pipes. The water wants to balance itself out (flow from high to low). The voltage is the pressure, the diameter of the pipes is the resistance and the flow rate is the current. Your flow is from top to the bottom always.

    Forward bias p-n junctions in semiconductors connect the p to the positive and the n to the negative. Think of a diode as a kind of valve is the water analogy.
    ZenerDiagram.jpg
    When connected in forward bias they are relatively easy to open, they need a bit of pressure to overcome the 'blockage'. If you were to reverse the polarity, by say flipping your battery around, it becomes very difficult to get any current flow through the diode.


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