Very simple series circuit question

[crazybandit]

Homework Statement

http://img2.imageshack.us/img2/6536/physics1.png

Homework Equations

I = V/R, R = R1+R2+R3+...

The Attempt at a Solution

2R+R=3R

V/3R

this is an SAT II physics practice question, i just want to grasp this concept so I am asking for an explanation, i.e. why this is a series circuit (or not?)

oh and how do i know to treat the section with the 1/2 R's as a parallel circuit and not the entire right side? don't they both have parallel resistors? how do i differentiate for circuits in general?

 

[rock.freak667]

Because if S₁ is left open then only a closed series circuit with V₁R,S₂ and 2R is formed.

 

[crazybandit]

Because if S₁ is left open then only a closed series circuit with V₁R,S₂ and 2R is formed.

so that means i add the 2R and the R to get 3R, hence V/3R, and that the right side is a series circuit? why is it a series circuit if they are parallel to each other? yet the 1/2 R's on the left side are treated as parallel?

 

[rock.freak667]

so that means i add the 2R and the R to get 3R, hence V/3R, and that the right side is a series circuit? why is it a series circuit if they are parallel to each other? yet the 1/2 R's on the left side are treated as parallel?

It is only because S₁ is left open that you can only consider the right side of the circuit only.

Sure the two R/2 resistors are in parallel but since S₁ is left open, no current flows through it, so you don't need to consider it.

Only consider where the current is flowing through. Which happens to be through R and 2R since S₂ is closed.

 

[crazybandit]

It is only because S₁ is left open that you can only consider the right side of the circuit only.

Sure the two R/2 resistors are in parallel but since S₁ is left open, no current flows through it, so you don't need to consider it.

Only consider where the current is flowing through. Which happens to be through R and 2R since S₂ is closed.

i know this, but never mind the question, how do i differentiate between a series and a parallel circuit? going back to the question, all the resistors are "parallel" to each other so how can i tell?

 

[rock.freak667]

i know this, but never mind the question, how do i differentiate between a series and a parallel circuit? going back to the question, all the resistors are "parallel" to each other so how can i tell?

If the same current passes through two resistors, then they are in series. If the current splits, then they are in parallel. I believe that is how it works, though I am not the best at circuit questions.

 

[crazybandit]

If the same current passes through two resistors, then they are in series. If the current splits, then they are in parallel. I believe that is how it works, though I am not the best at circuit questions.

oh ok, sidenote have you taken the SAT II physics?

 

[rock.freak667]

oh ok, sidenote have you taken the SAT II physics?

Nope. Only GCE A level physics a few years ago.