## 1.33 Part A

Rachel Wang
Posts: 49
Joined: Fri Sep 29, 2017 7:04 am

### 1.33 Part A

Here's the question:
The velocity of an electron that is emitted from a metallic surface by a photon is 3.6 * 10^3 km/s. (a) What is the wavelength of the ejected electron?

I tried doing this question two ways: once using the de Broglie equation, which gave me the right answer (2.0*10^-10m), and once using Ek = 1/2mv^2, which gave me the wrong answer (3.366*10^-8m).
I thought both of these methods would theoretically give me the same answer.

Is there a way to tell which equation is the right one to use?

Chem_Mod
Posts: 18693
Joined: Thu Aug 04, 2011 1:53 pm
Has upvoted: 616 times

### Re: 1.33 Part A

The problem is asking for wavelength. The former equation you used (the correct one) results in wavelength using the given velocity. The Ek equation results in energy, not wavelength. Even though it uses velocity, it does not tell you anything about the wavelength of the electron.

John Huang 1G
Posts: 46
Joined: Thu Jul 13, 2017 3:00 am
Been upvoted: 1 time

### Re: 1.33 Part A

I would use the Ek formula to solely determine the kinetic energy of the emitted electron. The de Broglie Equation allows you to determine the wavelength.

Abigail Urbina 1K
Posts: 102
Joined: Thu Jul 27, 2017 3:01 am

### Re: 1.33 Part A

Use the equation that directly includes wavelength, since that is the quantity you are looking for. The Ek formula should be utilized when you are looking for mass, velocity, or excess energy electron