# Voltage Divider Scenario Problem

Discussion in 'Electronics Homework Help' started by Rickel, Aug 9, 2013.

1. ### Rickel

1
0
Aug 8, 2013
A voltage divider circuit is to be constructed to obtain an output voltage 3 V (ptp) from an a.c. supply of 12 V (ptp). If the value of one of the available resistor pair is 6 kΩ, then what is the value of the other resistor with the output voltage across it is?

I would the 3v Be V2 in an equation where V1 would be 9 since the overal voltage going through is 12v? if so then i remember learning somewhere that V1/V2 = R1/R2.

i get the answer of 2kΩ only when i do: (v2)3/(v1)9= 0.33333333333 x 6kΩ= 2kΩ

so R2= 2kΩ BUT i wont get that if i did v1(9)/v2(3)=3??

2. ### Harald KappModeratorModerator

11,965
2,798
Nov 17, 2011
Sorry, I don't understand anything after the first question mark.

To go from 12V to 3V you need to divide by X (you'll sure find X yourself).
A voltage divider built from 2 resistors delivers Vout= R2/(R1+R2)*Vin.

If you know either R1 or R2 (and you do know one of the resistors because this value is given as part of the task description) you can find the other value using the above equations.

3. ### Rob_K

59
0
Sep 20, 2013
V1 is referring to your output voltage in your equation and V2 will be referring to your input voltage. So V1 will be 3 V, your desired voltage and V2 will be 12 V, the initial voltage from your power supply.

The 9 V value you are using is not part of this problem, I assume that you have tried 12 V - 3 V = 9 V. This is not useful in this calculation and is useful in learning only to know that this is not the right equation to use for a voltage divider. Try to think of it in terms of multiplication and division, not addition or subtraction, it's voltage divider not a voltage subtractor.

Hope this helps.