http://www.allaboutcircuits.com/worksheets/dc_sp.html

I'm looking at question 5, figure 6. Attempting to determine resistance between A & B.

I feel like there is probably something simple that I'm missing. That 470 ohm resistor is screwing me up.

I'm not looking for an answer (it's already provided, anyway). Can anyone give me a hint?

Thanks.

 

Does it help to point out that the 330 ohm resistor is in parallel with it?

 

Thank you for your response. I suspected as much but was taking a slightly different (and apparently wrong) tact. And now I have solved the problem and gotten the correct numerical answer.

330 is in parallel with 470 for an equivalent resistance of 193.875.
193.875 is in series with 220 for an equivalent resistance of 413.875.
413.875 is in parallel with 100 for an equivalent resistance of 80.54 ohms.

Though I don't think I truly understand one point.

Why is it not the case that the 330//470 is in series with 220//100?

 

Because the 100 is attached to the B terminal node and not the junction of the 220 and 330||470 junction.

 

Joe it now makes perfect sense. Thank you for the diagram. Funny if I had seen it drawn that way from the beginning I would have had no problem.

 

And that was the whole point.

You could have redrawn it starting at B and ended up with the same drawing ... and no confusion.

 

Sometimes a notepad is the best tool. Re-drawing of the circuit is often done to make things more 'readable'.

For instance, Ladder diagrams layout the circuit in an 'easier' to understand format.

http://www.allaboutcircuits.com/vol_4/chpt_6/1.html