Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Potential divider textbook example. Confused.

  1. Jul 23, 2016 #1
    DSC_0034.JPG DSC_0035.JPG Hi,

    I am just going through a textbook on electronics and have come across an explanation that uses potential dividers to work out potential values for resistors. I was wondering if anyone is able to explain how the author got the bit after "which can be written as": R1=(4.9/10.1)*R2

    How did he rearrange it to get this? Any help would be appreciated. Thank you! (I have added the pictures from the text book.)
     
  2. jcsd
  3. Jul 23, 2016 #2

    Baluncore

    User Avatar
    Science Advisor

    The same current flows through R1 as R2. The voltage across R1+R2 = 15V
    The voltage Vout across R2 = 4.9V
    So voltage across R1 = 15V – 4.9V = 10.1V
    The ratios R1 / R2 = 10.1V / 4.9V

    Therefore R1 = ( 10.1 / 4.9 ) * R2
    So maybe the second equation cannot be rewritten as R1 = ( 4.9 / 10.1 ) * R2
     
  4. Jul 24, 2016 #3

    jim hardy

    User Avatar
    Science Advisor
    Gold Member
    2016 Award

    That's algebra not electronics

    upload_2016-7-24_7-30-49.png

    solve for R1 ?

    There are several paths to get there
    i would

    1. divide both sides by 4.9
    2. multiply both sides by (R1 + R2)
    3. subtract from both sides R2

    and when you do that you'll find author's mistake
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted



Similar Discussions: Potential divider textbook example. Confused.
  1. Voltage divider (Replies: 4)

  2. Voltage divider (Replies: 15)

Loading...