Hello I'm a bit confused with potential dividers in one of my books it says:
The voltage is divided in the ratio of the resistances, so the larger value resistor has the greater voltage across it
Decreasing the resistance of the variable resistor causes the output voltage to rise
I dont get it, they are both contradicting eachother right please help!?
From John Wood
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- Thread Starter
- 20-06-2005 12:48
- 20-06-2005 14:41
>>The voltage is divided in the ratio of the resistances, so the larger value resistor has the greater voltage across it<<
True. V=IR, if I is the same and R goes up V must go up.
>>Decreasing the resistance of the variable resistor causes the output voltage to rise<<
But we are talking about a variable resistor set up in a potential divider situation. If you decrease the resistance by sliding the slider, you also increase the resistance of the other terminal! Remember is like having 2 resistors, slide the slider one goes up one goes down.
Lets say you have the slider in the middle you might have - 5ohms&5ohms. Slide the slider you might have 4ohms&6ohms. Slide some more your might have 3ohms&7ohms. Slide the slider all the way 0ohms&10ohms. So you can see one goes up one goes down.
- 21-06-2005 19:00
We'd better not have to know that for GCSE...My exam is tomorrow and I don't know what you're on about
- 21-06-2005 19:19
Its actually quite simple. Remember V=IR. The current flowing through a series circuit is constant. Soooo the only variable that determins the Voltage across the resistor (that is the difference in voltage between the two ends of the resistor) is proportional of the resistance.