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Homework Help: Electricity current question

  1. Dec 12, 2016 #1
    1. The problem statement, all variables and given/known data

    2. Relevant equations

    3. The attempt at a solution
    My thinking is that if the resistor's temp goes down then its resistance goes up. This means the current will bypass and ignore this resistor and the current around the circuit will stay the same?

    But this is wrong. The correct answer is:

    Resistance of parallel combination increases as temperature decreases
    Total resistance of circuit increases
    e.m.f./p.d. remains constant therefore current decreases

    What's incorrect in my knowledge?
    Last edited by a moderator: Dec 12, 2016
  2. jcsd
  3. Dec 12, 2016 #2


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    Gold Member

    You need to go back and study the basics of series and parallel circuits since you seem to not quite get the way parallel resistors work.
  4. Dec 12, 2016 #3


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    Staff Emeritus
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    Gold Member

    Consider the total resistance through the parallel pair. What happens to the total parallel resistance as one of the resistors changes. Write out the formula for the total resistance for a parallel pair. Compare the two different states (hi/low resistance). What happens to the total circuit resistance?
  5. Dec 12, 2016 #4
    I'm so stupid. I wasn't treating the thermistor as another resistor for some reason. I thought it was another circuit element with different properties.

    But yes, if the thermistor's resistance goes up, then that in combination with the 40 ohm resistor will form a bigger resistance.

    Then that in combination with the 80 ohm resistor will mean the circuit's total resistance has increased.

    And a bigger resistance means a reduction in the current flowing around the circuit.
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