# Homework Help: Analog to Digital Converter (ADC)

1. Oct 12, 2009

### Selwin

Hello,

I do not know if it's really upper physics but I have some exercices to do and I find them a bit difficult for a beginning.

This is a circuit: http://up.sur-la-toile.com/iu7M

I'm asked to simplify it like shown on the drawing so that afterwards I get this circuit: http://up.sur-la-toile.com/iu7L

I can simplify it by following the instance but I just would like to know what formula was used to simplify the circuit.

2) Then I have to determine the relation between r and R; Va7, E and R then i'm supposed to deduce I7. This is what I've done (using Kirchhoff's laws):

I7=Va7/2(R+r) is it correct ? However, I don't see the relation between r and R except maybe: E=(R+r)i....

Thank you for any valuable help!

2. Oct 14, 2009

### gabbagabbahey

Hi Selwin, welcome to PF!

This type of problem should probably be posted in the introductory section in the future.

When going from (a) to (b), you simply use the formula for two resistors in parallel. When going from (b) to (c), you use the formula for two resistors in series....do you see why?

Close, the EMF/voltage in the circuit is E-Va7. (E pushes the charges clockwise and Va7 pushes the counter-clockwise)

If you apply the method in the first diagram 7 more times, you should be able to easily express $r$ in terms of $R$.

3. Oct 27, 2009

### Selwin

Hello,

Sorry for my "short" silence and thank you for your reply gabbagabbahey.