+ Post New Thread
Results 1 to 5 of 5
  1. #1
    Junior Member level 1
    Points: 130, Level: 1

    Join Date
    Aug 2019
    Posts
    15
    Helped
    0 / 0
    Points
    130
    Level
    1

    Two Qs re: resistance

    Not sure if the answer depends on the circuit, or if this is a rule that will apply across the board?

    So, I get that a resistor will limit the flow of current in the circuit.

    I have a circuit with a 10k resistor, and let's say I add to that a 4.7k resistor. I believe this to be called 'piggybacking'?

    1. Is that considered series, or parallel?

    2. Why is the amount of current now decreased? To my complete newbie brain, there should be more resistance; to me, there is now 14.7k of resistance (+ or - a bit, due to tolerance). But apparently, there is now 5.3k of resistance. Why is that?

    Thanks in advance.

    •   AltAdvertisement

        
       

  2. #2
    Advanced Member level 3
    Points: 10,293, Level: 24

    Join Date
    Nov 2001
    Location
    US
    Posts
    894
    Helped
    310 / 310
    Points
    10,293
    Level
    24

    Re: Two Qs re: resistance

    If the two resistors have one terminal in common, then it is series connection and current will reduce if the voltage across the series connection stays the same as it was when only one resistor was connected.
    If the two resistors have two terminals in common, then it is parallel connection and under the same circumstances as above, the current will increase.



    •   AltAdvertisement

        
       

  3. #3
    Super Moderator
    Points: 264,236, Level: 100
    Awards:
    1st Helpful Member

    Join Date
    Jan 2008
    Location
    Bochum, Germany
    Posts
    46,168
    Helped
    14041 / 14041
    Points
    264,236
    Level
    100

    Re: Two Qs re: resistance

    Where did you get 5.3k? Resistance of parallel circuit is 10*4.7/(10+4.7) = 3.2k.



    •   AltAdvertisement

        
       

  4. #4
    Junior Member level 1
    Points: 130, Level: 1

    Join Date
    Aug 2019
    Posts
    15
    Helped
    0 / 0
    Points
    130
    Level
    1

    Re: Two Qs re: resistance

    Quote Originally Posted by sutapanaki View Post
    If the two resistors have one terminal in common, then it is series connection and current will reduce if the voltage across the series connection stays the same as it was when only one resistor was connected.
    If the two resistors have two terminals in common, then it is parallel connection and under the same circumstances as above, the current will increase.
    Ok, that helps.

    Quote Originally Posted by FvM View Post
    Where did you get 5.3k? Resistance of parallel circuit is 10*4.7/(10+4.7) = 3.2k.
    Well, where I get 5.3 is this: 10k - 4.7k = 5.3k

    But I see that's not the way it works. :)

    Thanks guys!



  5. #5
    Advanced Member level 5
    Points: 18,454, Level: 32
    Achievements:
    7 years registered

    Join Date
    Nov 2012
    Posts
    3,269
    Helped
    816 / 816
    Points
    18,454
    Level
    32

    Re: Two Qs re: resistance

    I have a circuit with a 10k resistor, and let's say I add to that a 4.7k resistor. I believe this to be called 'piggybacking'?
    Each resistor has two ends. It is a symmetrical device in the sense that you can exchange the two ends without ANY effect.

    Let us label the two ends of resistor R1 as E1 and E2. Same way label the two ends of resistor R2 as E3 and E4.

    If you connect E2 to E3 and keep the two free ends E1 and E4, you get s series connection. In a series connection, both resistors takes the same current (consider current like a fluid).

    If you connect E1 to E3 and also connect (independently) E2 to E4, and use the two ends (E1E3 junction and E2E4 junction) you get a combination that is called parallel (the two resistors are now lying side by side).

    In a parallel connection, both the resistors see the same voltage (but take different currents).

    In a series connection, the equivalent resistance is greater than the individual values. In a parallel connection, the equivalent resistance is smaller than the individual values.



--[[ ]]--