Quiz Help

Discussion in 'Homework Help' started by BirdMan, Oct 9, 2010.

  1. BirdMan

    Thread Starter New Member

    Oct 9, 2010
    4
    0
    New here but I will defintely stick around. This site has already been very helpful and the people seam real nice.

    Bit about me:

    Im 25 and in my first semester of a associated degree majoring to be a electrical technician within the energy systems sector.

    For some reason I am second guessing my answer to this problem. Is the answer simply VT which I figured out to be 46.78v?

    The given problem was in black and my answers are in red.
     
    • hw.png
      hw.png
      File size:
      23.6 KB
      Views:
      22
  2. bertus

    Administrator

    Apr 5, 2008
    15,648
    2,347
    BirdMan likes this.
  3. BirdMan

    Thread Starter New Member

    Oct 9, 2010
    4
    0
    I am very aware of the characteristics of series and parallel circuits. Well kinda... lol

    I figured IT by finding RT and VT.

    Im not sure if this is just a weird electronic coincidence but adding up all the current from all three resistors and dividing by three gave me a number real close to my IT.
     
  4. bertus

    Administrator

    Apr 5, 2008
    15,648
    2,347
    Hello,

    So you know Ohms law.
    Then you can calculate the voltage across each resistor using the values of them and the total current.

    Bertus
     
  5. Markd77

    Senior Member

    Sep 7, 2009
    2,803
    594
    You've got the right current and voltage for R3, but you need to use that current to calculate the other 2 voltages.
     
    BirdMan likes this.
  6. BirdMan

    Thread Starter New Member

    Oct 9, 2010
    4
    0
    I done that also with R1 being 18.2v R2 16.7v R3 11.8.

    It equals 46.7v.

    My question is: What is the highest voltage I can have with out burning up resistors? Is it the total voltage or is there a amount you can go over Vt?


    EDIT:

    Markd77 just made me have a bright light go off in my head. Since that is the smallest resistor I need to use that current amount because if i use any higher current in series it will blow that resistor? Am I right?
     
  7. Markd77

    Senior Member

    Sep 7, 2009
    2,803
    594
    I get about 14V for R1 with 27.5mA.
    As this is theoretical assume the resistors burn at their power ratings. In real life the power rating is more complicated but it's usually best to stay well below because they do get pretty hot at full rated power.
     
  8. BirdMan

    Thread Starter New Member

    Oct 9, 2010
    4
    0
    Thanks for the help. Great site and great help.
     
  9. Markd77

    Senior Member

    Sep 7, 2009
    2,803
    594
    If you've got about 36V for the answer then all is good.
     
  10. bertus

    Administrator

    Apr 5, 2008
    15,648
    2,347
  11. Georacer

    Moderator

    Nov 25, 2009
    5,142
    1,266
    If I were in your place I would try this method: You know that all the resistors share the same current (and should be as they are connected in series). You also know that the formula for power is P=I^2 \cdot R. So, I would use it for each resistor to find the maximum current that can pass through it. Then I would take the smallest of them, as it prevents all the resistors from burning up.

    Choosing that current, use the Ohm's law to calculate the voltage on each resistor, and sum them to find the voltage on the voltage source.
     
Loading...