physics a level

[bluetoon]

can anyone give me an explanation on this question.

Show that there are about 200 million atoms in the 20mm width of a postage stamp.

All help greatly accepted. i think it has to do with logarithmic scales and x10 powers

[jake-the-peg]

You're being asked to show you can estimate.

Estimate the volume of the stamp and divide by the volume of an atom

You'll need to use powers (standard form)

[Huderon]

It has more to do with the diameter of an atom than anything else. Atoms range in diameter from 0.1 to 0.5 nanometres. Now, since you are doing A level physics, your math is probably a lot better than mine, so you can do the calculation. Just remember to check which atom has the size you use, in case someone asks.

[Huderon]

er ... Jake, it's the width of the stamp that is being asked about, not the volume.

[scotman]

I agree.

If the question has been correctly stated here it is not answerable without assumptions of some other dimensions; unless it is a assumed to mean a linear string of atoms 20mm long.

[Calibax]

I agree Scotman, I think they're talking about a linear string since only one dimension is given.
The principle is the same though, divide the width of the stamp by the average diameter of an atom.

[jake-the-peg]

Oh yes so it is

Mine was a better question :c)

Doing it the other way dividing a 20mm stamp by 200 million. Is 2 x 10 to the minus 2 m. Divided by 2 x 10 to the 8 subtracting tHe power gives you 1 x 10 to the minus 10 m or about 10 nm

Justify this estimate, do the calculation the other way around and you're done

[Calibax]

If you have not been given the mean atomic radius in the question or in your text book, you may have to give consideration of which atoms make up the stamp. Being paper these would mainly be carbon, oxygen and hydrogen which would have smaller radii than say lead or gold because C H & O do not have the outer electron shells. This maybe venturing into the realms of chemistry rather than physics though.

[mibn2cweus]

Jake, wouldn't that be 0.1nm since a nm is 10-9m?

http://mimp.mems.cmu....ordofmag/dischart.htm

[beso]

Calibax //This maybe venturing into the realms of chemistry rather than physics though.//

It is all Physics because Physics is the fundamental science. Chemistry is a subset of Physics. Biology is based on Chemistry.

[bluetoon]

thank you all for your help. i looked for a measurement of a atom inside my text book and the only one i found was an atomic nucleus is 10*-12 of a meter (a picometer) but if i use it in a calculation i find the length of atoms in a line is too short by 100X (2 extra 0's)
not sure as this is the length of the nucleus given not the entire atom.

[bluetoon]

ahh i have just seen mibn2cweus's web link and i would like to thank you. this explains my error. Im sure i did not miss anything in my text book so i shall bring it up with my teacher.
Thank you all again

[Huderon]

Lord, you lot do like to make things complicated !

The smallest atom is about 0.1nm in diameter. So line 'em all up and there are 10 billion of them to the metre.

But as this needs to be done in mm, divide by 1000 and you get 10 million of them in one millimetre.

As the stamp is 20mm wide, multiply by 20 and you get 200 million across the width of the stamp.

I can't do math using powers, but a bit of paper and some crossing out of zeroes and a bit of multiplication got me there. I just thought that the OP should do some of the work for himself. The bit that took longest was finding that range of diameters and and finding out how many nanometres there are in a metre.

[New Judge]

If this is Physics A-Level (i.e. dividing one number by another) then it is little wonder that the rate of success is so good!

[mibn2cweus]

Seems to me the object of this question is to infer the average size of the atoms based on the number of atoms specified for the given width . . . do the maths.

[Huderon]

lol ... I don't have a calculator that will handle dividing 200 million into 2 !

But I did learn a few things getting to the answer.

New Judge, to be fair, I'm pretty sure that Physics A-level isn't all as easy as that, but as it's a very long time since I did any physics I can't say for sure. I do know that, for example, GCSE biology these days covers things that were A-level stuff 30 years ago. If that's true across all the sciences (and other subjects) the good results are down to good teaching and the kids putting in a lot of hard work.

[rov1100]

I've often wondered how they ever managed to split the atom when its in a continual state of movement. That was before the LHC I'm referring to.

[New Judge]

Actually I’ve found it to be the reverse, Huderon.

I took Physics at ‘O’ Level 45 years ago. Although I went on to take ‘A’ Levels I did not do Physics (2 or 3 ‘A’ Level subjects was the normal maximum then and I chose Maths and Chemistry). In 2007 I saw a (so-called) ‘A’ Level paper taken by my nephew. I won’t say passing would have been any great achievement as the pass rate that year was 95.2% and I imagine those who failed must have either not turned up or got their name wrong at the top of the paper. However I am quite convinced that with an hour or two of quick revision I could have achieved a decent grade (At least a C and possibly a B or even an A) with a paper set to that standard. It was no more difficult than the stuff I did at O Level and in many respects it was a considerably easier exam than my O Level.

This is plainly absurd. There is absolutely no way I should even get close to passing an A Level in a subject which I have not properly studied for 45 years and which I never studied at A Level anyway. My nephew went on to study Physics to degree level and during his first year I had to help him out with some of his assignments!

[jake-the-peg]

That's interesting NJ

Which a level paper did you try ?

I'm guessing it wasn't one on quantum mechanics or astrophysics.

My sons just finished A level and I couldn't manage that score blind on all the papers so I'm surprised.

I'd also be surprised if it were fields and further mechanic motion in a circle and all that

I' love to see this A level paper you found so easy what was the board?

[New Judge]

I don’t recall the Examination Board, Jake. No it certainly did not contain any questions on Quantum Mechanics (I had expected it to contain something like this and if it had I would have been stuffed). Nor indeed Astrophysics (with which I might have struggled, although I have acquired some knowledge of this subject over recent years). No idea what you mean by “...fields and further mechanic motion in a circle and all that” but again nothing of that nature as far as I can recall. I remember that I was confident I could adequately answer 60 or 70 per cent of the questions, which I found most surprising.

I’m surprised you had difficulty with the recent exam, especially bearing in mind your field of expertise. Perhaps things have changed in the last four years.

But I doubt it.

[theprof]

beso, I'm fascinated. So chemistry is "a subset of physics". In your dreams. Tell that to an organic or inorganic chemist and see how they respond.

Biology is "based on chemistry". Eh? Have the kindness to explain what you mean. What do you mean by "based" precisely? By the way, make it a convincing argument as I'm a professor of biochemistry with degrees, and higher education lecturing experience, in chemistry, organic chemistry, biology and biochemistry.

Tonight's question: Explain ecology in terms of chemistry.