basic voltage query

Discussion in 'Homework Help' started by Albert Symes, Oct 22, 2015.

Thread Status:
Not open for further replies.
  1. Albert Symes

    Thread Starter Member

    Oct 22, 2015
    41
    0
    got a question i cant find the answer to,can anybody help.cheers

    a 12v dc supply is connected to 2 100k resistors in series.a voltmeter has sensitivity of 10,000 per volt is swithed to its 10v range,

    calculate 1)voltage reading

    2) the percentage error of meter reading in part (1)
     
  2. StayatHomeElectronics

    Well-Known Member

    Sep 25, 2008
    864
    40
  3. Albert Symes

    Thread Starter Member

    Oct 22, 2015
    41
    0
    got a question i cant find the answer to,can anybody help.cheers

    a 12v dc supply is connected to 2 100k resistors in series.a voltmeter has sensitivity of 10,000 per volt is swithed to its 10v range,

    calculate 1)voltage reading

    2) the percentage error of meter reading in part (1)
     
  4. WBahn

    Moderator

    Mar 31, 2012
    17,743
    4,789
    10,000 what per volt? Cats? Geraniums?

    Since this is homework, you need to show YOUR best attempt to solve YOUR homework problem. It doesn't have to extensive or correct, but you need to give us something to start from. We aren't going to just work your homework for you.
     
  5. Albert Symes

    Thread Starter Member

    Oct 22, 2015
    41
    0
    12 x 10,000 ohm =120,000 /10 = 12000 v
     
    Last edited: Oct 22, 2015
  6. KeepItSimpleStupid

    Well-Known Member

    Mar 4, 2014
    1,144
    203
    It's not a well-formed question.
    e.g. The voltage across the 12 V source is 12 V/

    They probably want the voltage across one resistor. You also have to assume that the the voltage source is ideal. You can only measure one resistor at a time.

    So find the voltage across the resistor with no meter.

    Use the ohms/V relation to figure out what the meter's resistance would be at that voltage.
    ohm/V * Volts = ohms(meter)

    Calculate it again with the calculated resistance in parallel with 100K.
     
  7. WBahn

    Moderator

    Mar 31, 2012
    17,743
    4,789
    12 x 10,000 ohm = 120,000 ohm, it most certainly does not equal 1200 V.
     
  8. Albert Symes

    Thread Starter Member

    Oct 22, 2015
    41
    0
    your right,i humbly apologise for that mistake
     
    Last edited: Oct 22, 2015
  9. WBahn

    Moderator

    Mar 31, 2012
    17,743
    4,789
    Not a problem -- take another shot at it.

    Hint: Be sure to get the correct units for the meter sensitivity and then track the units through your work -- most mistakes can be caught that way.
     
  10. Albert Symes

    Thread Starter Member

    Oct 22, 2015
    41
    0
    12v x 10,000 ohm =120,000 /10 = 12000 v
     
  11. WBahn

    Moderator

    Mar 31, 2012
    17,743
    4,789
    Again,

    12 V x 10,000 ohm = 120,000 ohm

    It does NOT equal 120,000/10.

    Even if it did, 120,000/10 = 12,000 and NOT 12,000 V.

    And what is this 12000 V supposed to be? The reading on the voltmeter? Does that make any sense whatsoever?

    You haven't yet indicated how the voltmeter is connected to the circuit. Don't make us guess.

    What is the definition of the sensitivity for a voltmeter? What are the proper units for it?

    Don't guess -- look it up.
     
  12. Albert Symes

    Thread Starter Member

    Oct 22, 2015
    41
    0
    voltmeter has sensitivity of 10,000ohm per volt
     
  13. WBahn

    Moderator

    Mar 31, 2012
    17,743
    4,789
    Okay. So the sensitivity of your voltmeter is 10,000 Ω/V.

    Now, what does this mean? What IS voltmeter sensitivity? What does it tell you?
     
  14. JoeJester

    AAC Fanatic!

    Apr 26, 2005
    3,373
    1,159
    Here is your problem:

    on edit: Added one additional question.

    This happens to be a favorite question of mine.
     
    Last edited: Oct 22, 2015
  15. KeepItSimpleStupid

    Well-Known Member

    Mar 4, 2014
    1,144
    203
    I pretty much gave you how to do it. I just didn't do it for you.
     
  16. Albert Symes

    Thread Starter Member

    Oct 22, 2015
    41
    0
    100,000
     
  17. Albert Symes

    Thread Starter Member

    Oct 22, 2015
    41
    0
    thanks for the drawing,thats pretty handy
     
  18. JoeJester

    AAC Fanatic!

    Apr 26, 2005
    3,373
    1,159
    So ... What are the answers.

    You could have done the same drawing.
     
  19. Albert Symes

    Thread Starter Member

    Oct 22, 2015
    41
    0
    100,000 ohms

    and 10%

    I think
     
  20. WBahn

    Moderator

    Mar 31, 2012
    17,743
    4,789
    Don't just "think" up an answer. Analyze the circuit and determine the answer!

    And SHOW YOUR WORK!
     
Loading...
Thread Status:
Not open for further replies.