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Homework Help: Relationships between Current, Voltage and Resistance

  1. Jul 20, 2013 #1
    1. The problem statement, all variables and given/known data
    Based on the diagram attached, how do the values of current, I and voltage, V change when the sliding contact S of the rheostat is slowly moved from X to Y?

    2. Relevant equations
    Ohm's Law

    3. The attempt at a solution
    I used Ohm's Law to solve this question. My answer was: I decreases and V increases, because R is directly proportional to V and inversely proportional to I. As S is moved from X to Y, the resistance increases. I deduced that the voltage increases as resistance increases, and current decreases as resistance increases.

    However my answer was wrong; the correct answer was: I decreases and V decreases. I don't understand why the voltage would decrease as resistance was increased because Ohm's Law clearly shows that R is directly proportional to V. Can anyone please explain why?

    Attached Files:

  2. jcsd
  3. Jul 20, 2013 #2


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    2017 Award

    Staff: Mentor

    That is not true. You can re-write Ohm's law as RI=V. As you can see, V and I are proportional to each other. Another way to read R=V/I is "V and I have a constant ratio" (which is the same as "are proportional to each other").

    The total resistance increases, indeed.
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