Homework question #1

Discussion in 'Homework Help' started by cgeorge5150, Oct 8, 2009.

  1. cgeorge5150

    Thread Starter New Member

    Oct 8, 2009
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    0
    A 500 Ohm resistive load, that is consuming 30W of power, is connected in series with a protection resistor across a 220V DC source. Determine the resistive value and teh power dissipated in the protection resistor.
     
  2. hgmjr

    Moderator

    Jan 28, 2005
    9,030
    214
    Have you taken a stab at solving the problem yourself? If so, go ahead and post your attempt and we can assist you with any problems you may be experiencing.

    If you are stumped, then maybe you can describe what problems you are having setting up the problem.

    Also, you need to differentiate your posts by using a different title for each. Posts with the same title make it difficult for members to find the one they are assisting you with.

    hgmjr
     
  3. cgeorge5150

    Thread Starter New Member

    Oct 8, 2009
    9
    0
    I used I = sq root of (power/resistance) or sqr(30/500) = 250mA
    R=220V/250mA = 880 Ohm.
    P is 220V squared/880 = 55Watts
     
  4. JoeJester

    AAC Fanatic!

    Apr 26, 2005
    3,373
    1,159
    cgeorge,

    Kirchoff's Voltage Law applies.
     
  5. hobbyist

    Distinguished Member

    Aug 10, 2008
    764
    56
    First draw it up in schematic form

    W = I^2 x R
    W = E^2 / R
    W = E x I


    Then work with the equationS (plural) that has both variables in your schematic.

    Then you should see clearly what the voltage should be across the unknown resistor.
     
  6. mik3

    Senior Member

    Feb 4, 2008
    4,846
    63
    Hints:

    Calculate the voltage across the 500R resistor

    The resistors are in series so they have the same current
     
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