Fall 2013 Quiz Preperation Problem 10

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Ranger Saldivar 2D
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Joined: Fri Sep 25, 2015 3:00 am

Fall 2013 Quiz Preperation Problem 10

Postby Ranger Saldivar 2D » Mon Oct 12, 2015 1:08 am

For the problem, it states if molybdenum is irradiated with light of wavelength of 194 nm, what is the maximum possible kinetic energy of the emitted electrons, based on problem 9 molybdenum must absorb radiation with a minimum frequency of 1.09 x 10^-15 s^-1 before it can emit an electron from its surface. I calculated the minimum energy needed to produce this effect to be 7.22 x 10^-19 J. On problem 10 I used E=h(c/lambda). i converted 194 nm to 1.94 x 10^-7 m then used E=(6.62608 x 10^-34 Js) (2.99792 x 10^8 ms^-1)/(1.94 x 10^-7 m) and got (1.02 x 10^-18 J)-(7.22 x 10^-19 J) and got 2.98 x 10^-19 J instead of 3.03 x 10^-19 J.

Eduardogonzalez1G
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Re: Fall 2013 Quiz Preperation Problem 10

Postby Eduardogonzalez1G » Mon Oct 12, 2015 2:09 am

Everything is good until the last part. Instead of using 1.02 x 10^-18, leave it as 10.23 x 10^-19. Then you subtract 10.23 x 10^-19 and 7.22 x 10^-19.
If done correctly, you should get around 3.01 x 10^-19 J

Rachel Colbath 2G
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Re: Fall 2013 Quiz Preperation Problem 10

Postby Rachel Colbath 2G » Tue Oct 13, 2015 11:15 am

Do we keep track of sigfigs throughout the problem? ex. for the energy calculation I got for 1.023928759x10^-18
would I round that to 1.02x10^-18 considering it is limited by the given value 194 nm? Or do I plug in the whole value and only round according to sigfigs at the end. Also, I understand how you got 3.01x10^-19, but is that close enough to 3.03x10^-19 (the given answer)?

Caroline Chen 2A
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Re: Fall 2013 Quiz Preperation Problem 10

Postby Caroline Chen 2A » Tue Oct 13, 2015 11:55 am

Generally when doing problems, you should plug in whole values or at least values rounded past the number of sig figs given, so that at the end you have a more accurate answer without roundoff error. Then, round your answer according to the sig figs of the problem at the end. For the slight difference in answers, that might be from roundoff error.

Ranger Saldivar 2D
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Re: Fall 2013 Quiz Preperation Problem 10

Postby Ranger Saldivar 2D » Wed Oct 14, 2015 12:24 am

Why would I use 10.23 x 10^-19 if the least number of significant figures is 3 instead of 4?


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