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# Interview question

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#### ahmedragia21

##### Member
Hi, I've been asked a question in the interview but it was mainly related to physics and i've really forgot the thermodynamic physics , would someone try to explain the answer ?

Question
Let's say I have a .5 inch diameter silver hollow sphere, with a .028" wall thickness, and I want to heat the interior of the sphere to 365F ±.2 degrees, and maintain that temperature for approx 15 seconds. I want to power this mini oven with the smallest battery arrangement allowance space of .375: dia. x 2" length. The oven cycle will be manually activated/deactivated.

1. How would you best achieve heating the sphere?
2. Smallest battery arrangement/maximum number of uses/cycles.

I belive that the equations may be , Q = I*T , P=I*V , but i dont really know the equations for temprature (heat) to electricity .

#### bountyhunter

##### Well-Known Member
Is this a sphere that has to be heated from the outside or can you open it and put an element inside it?

FYI, the interior temp will not be constant, do you mean exactly in the center?

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#### ahmedragia21

##### Member
Is this a sphere that has to be heated from the outside or can you open it and put an element inside it?

I can put an element inside it.

do you mean exactly in the center?
Yes

#### RCinFLA

##### Well-Known Member
Not really a viable question. Is the sphere in air, what temp, pressure is air, is it in ice water, boiling oil, ....

What is inside sphere, vacuum, air, what temp, pressure is air, is it in ice water, boiling oil, ....

Being said it is certain thickness silver, I am guessing they want you to calculate resistance across opposite points on sphere.

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#### Boncuk

##### New Member
That question lacks precision! Don't try to answer it.

#### bountyhunter

##### Well-Known Member
Being said it is certain thickness silver, I am guessing they want you to calculate resistance across opposite points on sphere.
My thought also, which is why I pointed out an air filled object does not have a constant internal temperature if it is heated from the surface.

This:

heat the interior of the sphere to 365F ±.2 degrees

seems ridiculous considering there is no constraint on ambient temperature. I wonder if this is one of those "suicide questions" they ask at interviews to see if you will hang yourself.

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#### Mikebits

##### Well-Known Member
Well, if the interview is over, why do you care about the answer? Sounds more like homework to me. Be honest, it works better.

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#### ahmedragia21

##### Member
Mike, its not a homework, im graduated last year -_- .

I'm just caring to know the answer and present it here , maybe you know it .

bounty , yea its a very stupid question , but are there are any equations that solve this ? PDE ?

##### New Member
Well, if the interview is over, why do you care about the answer? Sounds more like homework to me. Be honest, it works better.

Come on, have you never not been able to answer something and been curious later what the answer would have been?

#### Hero999

##### Banned
If you think it's a stupid question then you should tell them, as long as you do so in a respectful manner and explain why you think it's a silly question.

##### New Member
If asked a question in an interview and not enough information is provided, it's best to ask for more information or to tell them that it cannot be adequately answered without that extra information. As bountyhunter suggested, maybe it's a "suicide question".

#### bountyhunter

##### Well-Known Member
If asked a question in an interview and not enough information is provided, it's best to ask for more information or to tell them that it cannot be adequately answered without that extra information. As bountyhunter suggested, maybe it's a "suicide question".
+1 Interviewers (and I have conducted MANY) learn far more from the questions coming back at them from the candidate than they do from answers. It is common to ask a confused or incomplete question to see if the candidate accurately picks up on it and requests you give them the missing information. That shows how they THINK. It's also common to make incorrect statements and watch to see if they know it's wrong.

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#### tcmtech

##### Banned
It's also common to make incorrect statements and watch to see if they know it's wrong.

I've had interviewers who later became bosses do that. Unfortunately with them it was not an interviewing ploy. They really didn't know what they were talking about!

Its also about that time I seriously assess the overall company, coworkers and management and determine realistically how far and how fast I can advance there. The next day is was typically when I turned in my two week notice!

#### arunb

##### Member
maybe the interviewer expected ahmedragia21 to explain why the question was absurd. Or perhaps they wanted to know how he would react to such a situation in real life.

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