PLEASE SOLVE these.. I cant get the solution..

Discussion in 'Homework Help' started by John Ramelb, Feb 2, 2014.

  1. John Ramelb

    Thread Starter New Member

    Feb 2, 2014
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    1.Two resistors A and B are connected in series across 220V DC source. When a voltmeter with a internal resistance of 10kΩ is connected across resistor A, the instrument reads 100V and when connected across resistor B, it reads 80V. Find Resistor A and B.



    2. A potential divider of resistance of 50Ω is connected across a 100V Dc source. A load resistance of 10Ω is connected across a tap in the potential divider and the negative terminal of the source. If a current of 4A flows towards the load, What is the current supplied by the source?



    PLEASE I REALLY NEED HELP SOLVE THESE TWO PROBLEM.. W/sol'n please thanks

    BTW WHO HAVE A PDF OF MCGRAWHILL BOOK IN ELECTRICAL CIRCUITS THANKS !!!
     
  2. bertus

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  3. spinnaker

    AAC Fanatic!

    Oct 29, 2009
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    Oh no homework is due and John wasn't paying attention in class again!

    When I was in school, these helped a lot:

    [​IMG]


    Always had one in my notebook.

    They have fancier ones now that I don't remember seeing back in the day:

    [​IMG]


    Looks like that site has some excellent explanations of Ohms Law BTW.

    http://www.electronics-tutorials.ws/dccircuits/dcp_2.html

    And you have the whole internet at your disposal today. Students today sure are lucky.
     
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  4. spinnaker

    AAC Fanatic!

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    Also the other thing that would help me is if I drew the schematic. I hate word problems. Pictures are so much easier to figure out.
     
  5. spinnaker

    AAC Fanatic!

    Oct 29, 2009
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    And there are simulators today to help out. Most people here like spice but a bit difficult to use. Yenka is a easy one to use but not the best for true accuracy. Probably OK for simple circuits and learning.

    Wow I wish I had all of those tools years ago.
     
  6. John Ramelb

    Thread Starter New Member

    Feb 2, 2014
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    @bertus
    @spinnaker

    Hello thanks for your reply
    I read the site that you give. Thank you.. I buy the book " Schaum's Outlines Basic Electriciy II Edition Milton Gussow" but I'm looking for the maybe the OLD Edition of that book 3000 Fully solved Problems in Circuits 1...


    Can you help me elaborate some facts that I want to know like the " internal resistance" because my Prof already explained the internal resistance only in the battery but I dont know in the Voltmeter,

    I have an idea solving the problem but I dont know if I doing it right. "hehe"
    My Engr. Prof. Didn't give the figure but some how i think this the figure In my own analysis.
     
  7. John Ramelb

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    Feb 2, 2014
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    In q.2 what is the potential divider resistance?
     
  8. bertus

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    Apr 5, 2008
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    Hello,

    The picture does not show to me.
    Please upload the picture to the forum:
    Attachments and Images

    Bertus
     
  9. John Ramelb

    Thread Starter New Member

    Feb 2, 2014
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    here is the image
    [​IMG]
     
    Last edited by a moderator: Feb 6, 2014
  10. John Ramelb

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    Feb 2, 2014
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    @bertus

    thats what i think in problem no. 1 ..thank you Engr.
     
  11. John Ramelb

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    Feb 2, 2014
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    @bertus
    @spinnaker

    sir/engr. what is a potential divider resistance?
     
  12. t06afre

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  13. John Ramelb

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    Feb 2, 2014
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    @to6afre

    THANK YOU . i Just read your reply

    thank you so much it is just like getting Voltage at Base in BJT


    thank you so much ENGR!
     
  14. John Ramelb

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    Feb 2, 2014
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    Thank you so much !!
     
  15. John Ramelb

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    Feb 2, 2014
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    ONLY THE q. 1 i only need explanation
     
  16. bertus

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    Apr 5, 2008
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    Hello,

    Looking at the diagrams, you have two voltage dividers:

    [​IMG]

    In the upper diagram, we have Ra in parellel with Rmeter, causing a voltage drop of 100 Volts across Ra.
    In the lower diagram, we have Rb in parallel with Rmeter, causing a voltage drop of 80 Volts accross Rb.

    With these two sets of parameters you can calculate tha values of Ra and Rb.

    Bertus
     
  17. John Ramelb

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    Feb 2, 2014
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    in Fig. 1 I use

    Vout = Vin ( RL / RL + Ra )

    100 V = 220 V ( 10k / 10k + Ra )

    Ra = 12k ohms

    for Fig. 2

    Vout = Vin ( Rb / Rb + 12k )

    Vout = 6.857k

    is this is correct my answers? THANK YOU SO MUCH SIR/ Engr.
     
  18. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    In the upper schematic Rb gets 10 mA more current as without the meter.
    With this higher current the voltage across Rb is 220 - 100 = 120 Volts.
    In the lower schematic Ra gets 8 mA more current as without the meter.
    With this higher current the voltage accross Ra is 220 - 80 = 140 Volts.

    Bertus
     
  19. MrChips

    Moderator

    Oct 2, 2009
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    You have two unknowns Ra and Rb.
    You have two situations which provide you with two equations.
    You can therefore use the two equations to solve for the two unknowns.
     
  20. shteii01

    AAC Fanatic!

    Feb 19, 2010
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    Problem 1.


    [​IMG]



    I came up with:
    Ra=2558.7 Ohm
    Rb=2450.5 Ohm
     
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