What is the relationship between resistors in a circuit?

[Matt O]

Homework Statement

I'm having trouble trying to find equivalent resistance. Here's a picture of some circuits I am trying to simplify (http://puu.sh/ngjMC/38160c3464.png)

For example, in circuit a, I can see that the 84 ohm and 105 ohm resistor are in series, and that can be simplified, but what do the markers A and B do to the circuit? Is the result of combining the 84 and 105 in parallel with the 63? And then what is the relationship of the 42 and the 21? Any tips on how to approach these problems are appreciated, thanks.

 

[cnh1995]

A and B are the points between which the equivalent resistance is asked. For a, I believe your approach is right. Go on combining two resistors at a time(either in series or parallel, whatever is correct).

 

[Matt O]

A and B are the points between which the equivalent resistance is asked. For a, I believe your approach is right. Go on combining two resistors at a time(either in series or parallel, whatever is correct).

But does it affect the resistance between 42 and 21? Are those in series still?

 

[Jake 7174]

The best way to find total resistance in circuits like these is to take it a step at a time and redraw after every step. you have combined the 84 and 105 and noticed that the result is in parallel with the 63. Find your equivalent resistance for those three then redraw. What further simplifications can you make? Eventually you will get to a single resistor.

 

[Matt O]

The best way to find total resistance in circuits like these is to take it a step at a time and redraw after every step. you have combined the 84 and 105 and noticed that the result is in parallel with the 63. Find your equivalent resistance for those three then redraw. What further simplifications can you make? Eventually you will get to a single resistor.

Okay, but do the marker points change anything? Is 42 and 21 in series or parallel in diagram a?

 

[cnh1995]

But does it affect the resistance between 42 and 21? Are those in series still?

They are not in series. Series equivalent of 84 and 105 is in parallel with 63. Their parallel equivalent is?? Can you further simplify?

 

[Matt O]

They are not in series. Series equivalent of 84 and 105 is in parallel with 63. Their parallel equivalent is?? Can you further simplify?

Ah okay I think Isee, so after that it is in series with the 42 and that combination is in parallel with the 21?

 

[Jake 7174]

Okay, but do the marker points change anything? Is 42 and 21 in series or parallel in diagram a?

The marker points do not change and do not worry about 42 and 21 just yet. Combine the 3 resistors and redraw the circuit. What else can you simplify?

 

[cnh1995]

Is 42 and 21 in series or parallel in diagram a?

They are neither in series nor in parallel directly. You need to simplify the circuit step by step and find out.

 

[cnh1995]

Ah okay I think Isee, so after that it is in series with the 42 and that combination is in parallel with the 21?

Right.

 

[Matt O]

Right.

Okay, makes sense. Thanks a lot for your help

 

[Jake 7174]

Okay, makes sense. Thanks a lot for your help

You can solve all of the circuits above by simplification alone except for the last one which is why it is a bonus. You will need to do a conversion first to solve that.

 

[Matt O]

You can solve all of the circuits above by simplification alone except for the last one which is why it is a bonus. You will need to do a conversion first to solve that.

Great, I've been working through them. What type of conversion are you talking about? I can tell it's not the same as the others

 

[cnh1995]

Great, I've been working through them. What type of conversion are you talking about? I can tell it's not the same as the others

Delta to star..

 

[Matt O]

Delta to star..

Hmm okay, I'll definitely look into that. Thanks everyone for the help

 

[Jake 7174]

Great, I've been working through them. What type of conversion are you talking about? I can tell it's not the same as the others

It is not the same in that you have resistors that are neither in series or parrallel

Hmm okay, I'll definitely look into that. Thanks everyone for the help

Star is also referred to as wye
One person may say half a dozen another may say six. They are the same thing.