# Relationships between Current, Voltage and Resistance

1. Jul 20, 2013

### fictionistruth

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
R=V/I

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?

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• ###### 2013-07-20 22.22.34.jpg
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2. Jul 20, 2013

### 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.