# Potential divider output deviance

#### Ezbee

Joined Nov 2, 2011
3
I have the following question to answer and apply.

What value of load resistance can this circuit supply before seriously deviating from the required 5v output? Justify this in theory, then prove with a practical measurement.

I just dont have any idea what to do and its frustrating because im sure its simple, can anyone help?

#### Georacer

Joined Nov 25, 2009
5,182
Could you post the exercise question exactly as it is given?

Which resistor is the load? Is it the 470Ω?
How much is "seriously deviating"? 5%? 10%?

Can you produce the formula for the output voltage?

#### Ezbee

Joined Nov 2, 2011
3
Could you post the exercise question exactly as it is given?

Which resistor is the load? Is it the 470Ω?
How much is "seriously deviating"? 5%? 10%?

Can you produce the formula for the output voltage?
The question as given was the second paragraph of my post.

I believe the 470Ω is the load and the deviating wasnt specified.

The circuit ive drawn isnt 100% accurate as ive just realised as the output V was actually about 4.9V as thats the closest I clould get with the resistors available to me.

The formula was Vout = Vin x (R2/Rtotal)

#### Georacer

Joined Nov 25, 2009
5,182
Do you mean you have a set collection of resistors from which you must choose your load?

The formula you posted is correct. You can use it to find the minimum and maximum acceptable load resistor.

Let's assume that a is the acceptable deviation.
The maximum load resistor is then given by the formula (1+a)Vout=Vin * R2/Rtotal.
The minimum load resistor is given by the formula (1-a)Vout=Vin * R2/Rtotal.

Can you find the limits for R2?

#### Ezbee

Joined Nov 2, 2011
3
Ah thanks for your help.

Its just dawned on me whats being asked.

I need to keep the total resistance the same and work out when the deviances occur when i change the R2 resistance.

Justify it in theory and then in practial.

Thanks alot, you help made it alot clearer to me.

#### Georacer

Joined Nov 25, 2009
5,182
You don't have to keep Rtotal constant. Replace it with R1+R2. With a given R1, both equations can be solved for R2.