I was just bouncing around LinkedIn (as you do) when I ran across a puzzle someone had posted with a simple caption of “Interview Question.”
This is one of those tricky little rascals that you either get right or wrong. Well, I guess that’s true of all problems of this nature. That’s not really what I meant.
What I was trying to say is that this is one of those problems whose presentation can easily lead you into looking at it from the wrong point of view, which subsequently guides you to an incorrect solution.
My knee-jerk reaction was that this puzzle wasn’t too difficult. Almost immediately, I saw that my friend Steve Leibson had posted the correct answer, which (to be honest) was no great surprise.
As an aside, did you see the column Steve posted today: A Brief History of PCBs: Where Did Printed Circuit Boards Come From? As is always the case with Steve’s writings, I learned all sorts of things I never knew before, but we digress…
Just for giggles and grins, I shared this little conundrum with a few friends by email, only to be surprised by the selection of incorrect answers I received in response.
Looking at these responses, it was obvious where each of my friends had gone wrong. It was also obvious that each had simply glanced at the circuit and then made an on-the-spot assumption upon which they had based their subsequent calculations.
What say you? Dare you resist?
1/3 Ohm
Correct 🙂
All three resistors connect to both the top rail and the bottom rail, putting them in parallel for a total of 1/3 ohm. But it took a second look to see that.
I love the way that simply presenting the diagram in this way is designed to cause confusion — if we just saw 3 resistors in // it would be easy — of course, this leads us to think of all the things that are unintentionally drawn in such a way as to cause confusion LOL
Three 1Ω resistors in parallel = 0.33333Ω.
You’ve got it — as I commented above, I love how this problem is drawn in such a way as to cause you to stop to think “just a moment…”
You could of course confuse things even more by asking “What current will flow?” Since there isn’t a battery, the answer is zero. Although the ohmmeter by definition must put some current through the resistors. So change the ohmmeter to an ammeter…..
Ooh! You are a tricky one Mr Ashton (I like that — I’ll use it the next time I’m presenting to some students). Do you remember my “Good Grief! Is that the Height?” column on EEWeb? https://www.eeweb.com/good-grief-is-that-the-height/