# Potentiometer question.

1. Nov 9, 2013

### brenfox

1. The problem statement, all variables and given/known data
A circuit shows a 10kΩ Pot with a 5k Ω load. Determine the position of the slider on the pot when the voltage across the 5kΩ load is 3 volts. The input voltage is 9 volts.

2. Relevant equations

3. The attempt at a solution Input voltage = 9 volts. Output voltage = 3 volts. Therefore the ratio of the resistance must be 3/9. Which equates to 1/3. So 10Ω/3 = 3.3Ω is the position of the Pot.
Am i on the right track? Any help would be appreciated.

2. Nov 9, 2013

### UltrafastPED

If by "output voltage" they mean the voltage at the node between the pot and the load ...

Then the 5k load is taking up 1/3 of the voltage, leaving 2/3 to the pot. So what is the resistance of the pot?

3. Nov 9, 2013

6.6k ohms?

4. Nov 9, 2013

### UltrafastPED

Have you studied voltage dividers?

Or you can just apply the Kirchoff Voltage loop rule.

5. Nov 9, 2013

### Staff: Mentor

There are several different ways the components could be connected. Is it one of these?

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6. Nov 9, 2013

### UltrafastPED

Really creative! I just assumed (d) - though I have seen most of the variations when assisting in the circuits lab.

7. Nov 9, 2013

### brenfox

It is circuit C. The voltage across the 10k pot is 9v. The voltage is 3 volts across the 5k resistor/load. Therefore positioning the slider at a certain point will result in the voltage output to be 3 volts. not sure how to determine this. voltage output = r1/r1+r2 which according to my calculations equals 6 kilohms. I am currently trying to get my head around kirchoffs law etc. I apologise for my lack of understanding. This is an open university course and i am struggling!

8. Nov 9, 2013

### UltrafastPED

So for circuit (c) the slider is positioned 2/3 of the way down - the 5k load is in parallel with the portion of the pot which is past the slider; that is, they both see 3 volts.

So the upper portion of the pot drops 6 volts. See your result from message #3.