URGENT! UNIT 8 practical application questions! 2-4!

Discussion in 'Homework Help' started by JulianXXX18, Sep 22, 2010.

  1. JulianXXX18

    Thread Starter New Member

    Sep 22, 2010
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    Im having trouble with these practical applications in unit 8. Here is question number 2:

    2 resistors are connected in series. one resistor has a resistance of 1000 Ω, and the other resistor value is unknown. the circuit is connected to a 50 volt power supply, and there is a current of 25mA flowing un the circuit. if a 1500Ω resistor is connected in parallel with the unknown resistor, how much current will flow in this circuit?
     
  2. Jony130

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    Feb 17, 2009
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  3. JulianXXX18

    Thread Starter New Member

    Sep 22, 2010
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    please explain ur equation again. i think im starting to get it.

    V = 25mA * 1000 = 25V

    so 1 volt = 25 mA? and 25 volts equals 1000 ohms?
     
  4. Jony130

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    Feb 17, 2009
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    You have two resistor connect in series.
    First R1 resistor is equal R1 = 1000Ω = 1KΩ second Rx is unknown.
    Thous two resistor are connect to 50V power supply.
    Total resistance of a circuit is equal
    Rtot = 50V/25mA = 2KΩ, and voltage on R1 is equal 25V.
    So the remain voltage of the supply voltage must be across Rx.
    So Rx = ??
     
  5. shteii01

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    Feb 19, 2010
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    You have a circuit with three elements connected in series. These three elements are: 50 V supply, 1k resistor, unknown resistor (RX). Current in this circuit is 25 mA. Since all the elements are in series, 25 mA passes through each element. Therefore:
    50V = 25mA(1k+RX)
    solve this for RX
     
  6. JulianXXX18

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    Sep 22, 2010
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    so the answer is 25 volts?
     
  7. Jony130

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    Yes 25V will be present across Rx resistor.
    So from Ohms Low Rx = 25V/25mA
     
  8. shteii01

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    Feb 19, 2010
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    That was step one. You now know all the elements that make your circuit. Using this information you can find current. You will have 50V supply in series with R1=1k resister in series with combination of RX=1k resister in parallel with 1.5k resistor.

    Simplify the two resistors in parallel (RX and 1.5k), that will give you one resistor in series with the R1=1k resistor. Simplify two resistors in series, that will give you one resistor. Use Ohm's Law to find current.
     
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