Question 34 from Photoelectric Effect Post Module Assessment

Kelly Kiremidjian 1C
Posts: 62
Joined: Fri Sep 29, 2017 7:04 am

Question 34 from Photoelectric Effect Post Module Assessment

Can anyone help me with question 34 from this post assessment? I said C for #33 which was correct but couldn't figure out #34. Thanks!

33. Molybdenum metal must absorb radiation with a minimum frequency of 1.09 x 1015 s-1 before it can emit an electron from its surface. Answer the following two questions.
A. What is the minimum energy needed to produce this effect?

A. 4.51 J

B. 7.22 x 10-12 J

C. 7.22 x 10-19 J

D. 1.15 x 10-19 J

E. None of the above
1/1 point

34. B. If molybdenum is irradiated with 194 nm light, what is the maximum possible kinetic energy of the emitted electrons?

A. 6.41 J

B. 3.05 x 10-19 J

C. 1.03 x 10-11 J

D. -5.58 x 10-19 J

E. None of the above

Sabrina Dunbar 1I
Posts: 57
Joined: Fri Sep 29, 2017 7:07 am
Been upvoted: 1 time

Re: Question 34 from Photoelectric Effect Post Module Assessment

Hi Kelly,
After finding the threshold energy in #33 to be 7.22x10^-19, you must look back at the equation hv(aka E)-phi=1/2mv^2. Phi is 7.22x10^-19 and because E=hc/lambda, you can calculate the energy of the photon to be 1.02x10^-18. Then, plug those two numbers into the above equation and you will get the max kinetic energy to be 3.05x10^-19. Hope this helps!