## Fall 2013 Quiz Preperation Problem 10

Ranger Saldivar 2D
Posts: 28
Joined: Fri Sep 25, 2015 3:00 am

### Fall 2013 Quiz Preperation Problem 10

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
Posts: 29
Joined: Fri Sep 25, 2015 3:00 am

### Re: Fall 2013 Quiz Preperation Problem 10

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
Posts: 30
Joined: Fri Sep 25, 2015 3:00 am

### Re: Fall 2013 Quiz Preperation Problem 10

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
Posts: 20
Joined: Fri Sep 25, 2015 3:00 am

### Re: Fall 2013 Quiz Preperation Problem 10

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
Posts: 28
Joined: Fri Sep 25, 2015 3:00 am

### Re: Fall 2013 Quiz Preperation Problem 10

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