## Module Post Assessment 33

GFolk_1D
Posts: 101
Joined: Fri Aug 09, 2019 12:15 am

### Module Post Assessment 33

Molybdenum metal must absorb radiation with a minimum frequency of 1.09 x 10^15 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?

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

I solved A to be 7.22 x10^-19 J but am unsure how to go about part B. Thanks!

Lindsey Chheng 1E
Posts: 110
Joined: Fri Aug 30, 2019 12:16 am

### Re: Module Post Assessment 33

GFolk_1G wrote:Molybdenum metal must absorb radiation with a minimum frequency of 1.09 x 10^15 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?

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

I solved A to be 7.22 x10^-19 J but am unsure how to go about part B. Thanks!

We know that E(k) = E(photon) - E(threshold) and that the definition of Threshold Energy is the minimum energy needed to emit an electron from a metal surface. In the previous question, we actually solved for the threshold energy, and found that it was 7.22 x 10^-19 J.

Now, the only missing information for this equation is E(photon). So we use E(photon) = hv = (hc)/lamda to solve for it, where the wavelength is 194/10^9 m. After solving for E(photon), you can plug it into E(k) = E(photon) - E(threshold) and you should get 3.05 x 10-19 J. Hope this helps!