Open Resistors

Discussion in 'Homework Help' started by MeltedOzark, Nov 8, 2011.

  1. MeltedOzark

    Thread Starter New Member

    Nov 8, 2011
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    Hello electrical enthusiasts, my friend and I require assistance for our electronics class.

    We have to find the voltage drops in a series circuit with 5 resistors, the 3rd of which is open. Now, as far as I know, this resistor gives infinite resistance, so we don't understand how we calculate current for the circuit (the only method we know being V/R).

    Now, our knowledge on circuits is extremely limited, so it would be greatly appreciated if someone explains this in simple terms. Thanks in advance for any help :D
     
  2. Adjuster

    Well-Known Member

    Dec 26, 2010
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    You already have a valid formula for the current in the circuit: I = V/R.

    As you say, if a resistor is open, it has infinite resistance. What then is the circuit current?
     
  3. crutschow

    Expert

    Mar 14, 2008
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    Hint -- The question is: where does the voltage drop occur and how much is it?
     
  4. MeltedOzark

    Thread Starter New Member

    Nov 8, 2011
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    The question asks for the voltage drops at all the resistors, but if the current is zero, there aren't any voltage drops?(meaning its a trick question). Or just a big drop at the battery? As the total voltage for the circuit is 24V.
     
  5. praondevou

    AAC Fanatic!

    Jul 9, 2011
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    You are almost there.

    If the current is zero then there are no voltage drops on the resistors that are not broken. V=IxR

    Now I wonder how we could solve the voltage drop on the broken resistor with the formula V=IxR. :D Is that zero multiplied with infinite?

    If the total voltage is 24V and there is no voltage drop on the intact resistors then the total voltage appears at: ?
     
  6. crutschow

    Expert

    Mar 14, 2008
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    Or: If you put a voltmeter across each resistor, one at a time, what would you measure for each resistor?
     
  7. MeltedOzark

    Thread Starter New Member

    Nov 8, 2011
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    So the voltage drop at R1,2,4,5 is 0, while R3 is 24?

    If that's correct, I totally understand it, and I thank you gentlemen :p
     
  8. praondevou

    AAC Fanatic!

    Jul 9, 2011
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    That's it.
     
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