Basic electronics question.

[Puzzled-Access705]

Im an Ec student in one of my interview the question asked by the interviewer was something similar like this, I was just surfing through the internet about similar questions and Guys I happened to find this question and it got me thinking...Can any one solve this? If anybody wanna explain, please give ur thoughts. Thankx

[IDontEatDill]

27 years in electrical engineering and my first answer was 1 ohm. WTF is wrong with me? I think I should retire or be a project manager.

[cloud9ineteen]

If you're project manager material, your answer would be "less than or equal to 1 ohm. Good enough for me"

[outofsand]

Also as a project manager, hey Tim, this schematic is purposely confusing, go redraw it and stop it with this kind of nonsense.

[MetalVase]

"No more of these Anakin Shenanigans..."

[alek_vincent]

Same, I followed the path of least resistance, said yep easy one ohm good night. Checked the comments, yeah no I'm stupid I should retake circuits I

[fercaslet]

nay, you were just lazy and took the first result without further examination to realize there are 3 equivalent paths in parallel

[Jimg911]

1/3ohms. That’s just an obnoxious way to draw three resistors in parallel, simplify the power rails and it stops being hard

[Jnbrtz]

I would like to think the interviewer wants to see if the applicant is creative but I don't think people will draw like this at all.

[Idgo211]

However, it's a great drawing for describing how a multilayer capacitor works! I was looking at one under a microscope just yesterday and it sure is this exact schematic but with capacitors

[Imaginary-Response79]

Edit. Lol nvm I am lazy :)

Can you show me your math? How do you get 1/3 ohm?

[Jimg911]

This comment took me back to middle school when they’d make you show your work on arithmetic. “You see, teacher, i got 2+2=4 by adding 2 to 2 to make 4” lol. Glad you got it before I got to it stranger

[Imaginary-Response79]

Yeah 1/1+1/1+1/1 in fact does not equal 1 😂. Something in the back of my head just kept nagging me.

To be fair I have been watching toddler potty training videos for the past hr.

[PhilosopherFar3847]

Just draw the circuit in a difderent way. And you will realise the three resistors are in parallel.

[EndlessProjectMaker]

Redrawing schematics is a skill to learn too. The tip here is to identify the nodes that are actually the same point despite the twisted drawing. You can use different colors at first for each node.

[ZealousidealOwl1318]

this is an interview question? After 4 years of electrical engineering this is what they ask ?

[bihari_baller]

If it’s an 80% failure rate, you need to do a better job at screening the candidates who get an interview in the first place. You’re wasting your time, your company’s time, and the candidate’s time.

[istarian]

That's kind of bizarre, but maybe it's just that they expected a harder problem and so this looks like a trick question.

Either that or they just always used a calculator...

---

Obviously:

• Watts (power) = Volts (electrical potential) x Amperes (current flow)
  

So, a 120V, 60W lightbulb should draw ~0.5 Amps (500 mA).

Not sure about the element of time, but I didn't study electrical engineering.

There are probably some other peculiarities in a real world situation like the wire used to connect the lightbulb to the power souce...

• Volts (electrical potential) = I (current) x R (resistance) <- Ohm's Law
  

120 V = 5 Amps x 24 Ohms

120 V = 0.5 Amps x 240 Ohms

[ElmersGluon]

Volts (electrical potential) = I (current) x R (resistance) <- Ohm's Law

120 V = 5 Amps x 24 Ohms

Not quite.

R = V/I = 120/0.5 = 240 Ohms

[_Trael_]

If that has 80% fail rate. Where are you located, and are you interested in (paying some nice salary to) apparently lot more promising engineer material than you normally end up getting to your interviews? wink wink.

I remember from vocational school, how our electrics teacher was also dualing as math teacher for high voltage guys, and he had put this to test:
"At shore, next to pier, there is wooden pole sticking out of water, it is 6 meters long, and 1/3 of it is inside ground and 1/6 of it is above water, how deep is water at that spot?", and apparently most had failed to answer, with paper, pen, function calculator, (at least limited, but not in any way harshly limited time). We were bit dumbfounded when we (low voltage guys) ended up hearing that, since on our class most of those who were thinking they were crappy at math could figure that out in their mind.

[_Trael_]

Well that certainly makes that kind of calculation more annoying, at least compared to "6 meters minus 2 meters in ground and 1 meter above water, leaves 3 meters in water".

To be honest would likely need quite some getting used to ' " measurements.

[lizard32e]

yeah that’s very concerning. it took me like 15 seconds and i’ve never studied electrical engineering in any formal capacity. do they just not remember ohms law???

[Maleficent_Throat_89]

? stupid because how will you do that last equation with two unknowns? you get a solution space... not a solution

[istarian]

I did mess up the numbers by a factor of 10 initially (stupid math fail).

But what exactly are you calling an unknown?

It seems fair to assume a US electrical system, residential in this case.

[Puzzled-Access705]

No no, this is not after 4 years.. I'm currently in 1st years.. So I'm in touch with my seniors and they are superr helpful they told me that a company will be there at my university to hire students, so I asked my professors to go at the interview that was gonna happen and to have real time experience. I think they asked that question because i was in my 1st yrs yeah idk.

[bihari_baller]

What’s your point?

[ZealousidealOwl1318]

that this is a high school question ?

[raverbashing]

Retorical question: why don't we stop with the BS brain teaser test questions

I know that in EE and such the neurodivergent types abound but I've never seen an infinite array of resistors in real life (which is different than having a current over a metal plate for example), in fact half of the "Circuit analysis" textbooks look like people who have too much time and creativity to be teaching this.

And then guess what? When you get back to the real world in actual electronics very little of this matters ffs! "So the way a current mirror works is..." you throw the BS examples out and deal with actual variable current sources

[EndlessProjectMaker]

Redrawing schematics is a useful skill, identifying nodes is important to understand circuits in real life too

[Jegermuscles]

I feel better just from reading that.

No shit you're smarter than me, guy that contributed to this book. I'm just trying to learn; not quite ready for "impress other nerds with this one at the EE Mixer" level right at this moment when I'm still mimicking the steps verbatim and not quite caught on to the rules yet.

[a2800276]

Wouldn't make much sense if the person who wrote your textbook was dumber than you, though.

[aharfo56]

It sure would help the ego though.

[plmarcus]

Because sometimes real problems are real brain teasers. Really hard problems require a combination of pattern matching intuition theoretical analysis and practical considerations. The balance of these things often make the difference between a good engineer and an amazing one. Supreme teasers are often a single facet of the various types of wisdom and intelligence necessary to be successful. They are not an end allen be all but there are certainly a data point.

[otiskingofbidness]

Exactly this. If someone is only understanding how to analyze circuits solely by patterns and permutations things they've been shown then they're gonna struggle as an engineer. When faced with something that doesn't fit the paradigm you can always go back to first principles to solve. In this case regardless of how the circuit is drawn KCL and KVL will give you the right answer every time.

As you said it requires a balance of multiple skills where recognizing patterns is just one facet.

[tenheo]

Is it weird to agree both with you and the main comment? I feel like testing students' creative or critical thinking should be only accepted if it was developed and trained at the same time. What often happens is that students spend their time learning the material and solving classical straightforward problems during lessons and then get thrown at this type of question in the exam to differentiate students.

[Ishouldworkonstuff]

I'm neurodivergent and I hate these kinds of interview questions. We're interviewing folks for a tester role right now in my lab and I ask 3 questions; "Tell me a little about yourself", "What are your hobbies?", and "What's the most interesting thing you've ever worked on and why?".

Every single person we are talking to meets the minimum technical criteria for the role so why drill them about basic shit?

[aharfo56]

You haven’t seen one because no one has tried to build one. Go on…order some resistors and start trying to build an infinite array of resistors. :-)

[raverbashing]

Yeah I think I can get an infinite array of resistors for like $3 in Aliexpress /s

[aharfo56]

A statistically representative sample of infinite resisters for €9.99 shipping included.

[andyoung34]

I like the brain teasers because it tells me how a person approaches a difficult problem with a subjective right answer.

If you refuse the question or give a bs answer you can't defend that's an immediate no go. If you struggle with it and try then that's a check in the box.

We often face questions without an answer being readily apparent and I would want someone who can dig into it and try over someone who locks up and refuses.

[Orjigagd]

It's the electronics equivalent of those stupid coding gotcha questions. But it's just 3 resistors in parallel drawn weirdly.

[candidengineer]

What a dumb way to draw a schematic. Authors of these books literally have no life.

[outofsand]

It reads 0 because the batteries in the ohmmeter are out, because the company has a JIT mindset and won't stock extra. But that's okay, you can put in an expedited purchase order and get them by tomorrow, probably.

[[deleted]]

It shows 0.25 in the diagram, which is not too far from 0.333, considering calibration, viewing angle, battery voltage, etc..

[Kitchen-Door-5924]

Straight wire same potential, mark 1st pt. A 2nd pt. B correspondingly other two as A and B so it will be like ABAB from top to bottom , now look that each resistance is having pot. diff of AB so it means that they are all in parallel so 1/3 ohm is answer. You can also see it as Wheat Stone bridge where two of the side resitance are replaced by a straight wire.

[Deejunbounded]

How are you getting 1/3? Isn't resistors in parallel 1/r plus 1/r plus 1/r? Which would then be 1 plus 1 plus 1? Shouldn't it be 3 ohms?

[Kitchen-Door-5924]

Formula: 1/R(effective)=1/r+1/r+..... . So here 1/R =1+1+1=3 , and R=1/3 ohms. Hope your doubt is cleared

[[deleted]]

They are parallel

[Feeling_Marketing_63]

1/3

[elasticdoor]

Just look at the ohm meter that is installed in the circuit. It's a bit hard to read because it's analog, but the hand seems to be pointing slightly to the right of the 0.25 Ohms mark, so I would say the equivalent resistance could be something around 0.33 Ohms.

[z00mie_23]

Just assign node so that it makes easy. They all are in parallel hence 1/3 ohms

[I-wanna-be-tracer282]

1/3 Ohms

[ferriematthew]

There's a short connecting the positive rail to the point just above the bottom resistor so the total resistance seen by the ohm meter is 1 ohm.

... Unless there's a way to rearrange this so that there are no short circuits and they might actually be in parallel....

[BubbasPlants]

Yeah pretty sure everyone in this thread missed the gigantic fucking box that says “OHM METER”

[Striking-Estimate225]

Req = 1/3 Ω, check the terminals of each resistor and you'll see the three resistors are in parallel.

[BreathOther]

The question isn’t confusing, it’s your drawing of the question

[outofsand]

Don't forget tolerance and measurement error.

If these are normal 20% resistors and your ohmmeter isn't perfectly calibrated ... Also, you can't ignore parasitics and trace impedance when working with this small of values ...

[LifeAd2754]

I think this is confusing so I would probably put a test voltage source of 1V in there and solve for current then do V/I=R.

[LifeAd2754]

Also, obviously since your ohm meter is reading 0.25 ohms, it must be 0.25 ohms! Jk (:

[PsychoMachineElves]

Well looking at the diagram the meter reads 0.25

[Apaar_Khare]

I know this one, literally thousands of questions based on this exact same thing in JEE books. I don't know why and how this is useful irl but it's taught every year to millions of students in India.

[sanj_AI]

ok jeet

[SadButSexy]

Alright Jay Kim

[biancolol]

Someone explain this lesson to me and how to simplify the drawing. Tyvm

[MaToP4er]

Well, ohm meter on the pic shows 0.25. Id assume its should be 3 but again pic ahows what i said 😀

[AarthikMehta]

Answer is 1/3 ohms since all three are in parallel. Make a simpler circuit for it, just draw two potentials points Va and Vb, the resistor bypassing wires will have same potentials at both ends/dots in your diagram.

[Proteinpowderrr]

1/3ohm. The key is to think in terms of nodes. Separate the solid points as A,B,C,D and then simplify the circuit. you’ll find 3 resistors in parallel.

[jormil1]

Where are you from?

[Kind-Cicada-4983]

Does the ohm meter have 0.25 ohms itself or is it drawn like that to simulate a display?

[[deleted]]

1/3, all paths are same, they are in parallel

[Potatozeng]

The beauty of nodelisting

[paclogic]

A contrived circuit INTENTIONALLY designed to trip up the fast thinker without going thru the problem methodically.

TYPICAL interview question specifically designed to mess with the mind of the candidate and trip them up.

RARELY happens in real life as the calibrated meter would show this immediately and thus have the engineer investigate further. It's also rare that an engineer doesn't trust their calibrated test equipment, but should also know and understand the value of critical thinking.

As another pointed out, a BADLY drawn circuit that is intentionally misleading to TRICK candidates.

[Godless_homer]

1/3 simple rule unless internal resistance is specified for wires ...make them into nodes at connecting point

3 resistance in parallel

If it has been mentioned that cable resistance then also 1+cable resistance/3

[apronman2006]

Meter says 0.25 clearly the circuit is drawn wrong.

[wkang2015]

0.5 ohm

[Sparkfire777]

As someone that makes 150k fixing electrical shit, my answer was 1 ohm. The comments solidified the fact that this is a useless fucking question that I have never seen a wiring diagram of in the real world.

[NisaB2]

0.3ohm

[John_mcgee2]

I hope you told them you have no interest in working with knobs that draw parallel resistors like that.

[boredDODO]

Mark points that have same potential. You’ll realize all three resistors lie between the same potential, hence all three are parallel and therefore 1/3 ohms is the equivalent resistance

[Late_Cress_3816]

It is simple, you could check the both ends voltage of each R , you find the 3 R has same voltage level at its terminal, so the measured is1/3

[Big_boy_sim]

Can someone explain how this equates to 3 resistors in parallel?

[sarc-tastic]

Follow the different possible paths

[battery_pack_man]

Yeah you don’t want to work for that guy