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### Dino Nuggets Problem 8b

Posted: **Fri Nov 01, 2019 1:01 pm**

by **ValerieChavarin 4F**

8. B) A newly designed laser pointer with a certain frequency is pointed at a sodium at a sodium metal surface. An electron is ejected from the metal surface with wavelength 1.10nm. What is the frequency of the light from the laser pointer? The work function of sodium is 150.6 kJmol^1.

I understand that since the wavelength of the electron was given, which has mass, we would use the DeBroglie Equation. However, I am confused about how to incorporate the work function as I can't seem to cancel the proper units out.

### Re: Dino Nuggets Problem 8b

Posted: **Fri Nov 01, 2019 1:16 pm**

by **MingdaH 3B**

For this equation, you'd find the energy of the ejected electron, add that to the work function and now you'd have the total energy of the laser. From there, use E = hv to find the frequency.

### Re: Dino Nuggets Problem 8b

Posted: **Fri Nov 01, 2019 1:25 pm**

by **ValerieChavarin 4F**

I got that far, as to find the Energy of the ejected electron, but how do I cancel the mol^-1 of the work function to be able to add it to the

?

### Re: Dino Nuggets Problem 8b

Posted: **Fri Nov 01, 2019 10:36 pm**

by **alicechien_4F**

You multiply by Avogadro's number since you're looking for the energy of a single electron, not a mol. That way, the units will also cancel out. Hope this helps!

### Re: Dino Nuggets Problem 8b

Posted: **Sat Nov 02, 2019 3:02 pm**

by **Simon Dionson 4I**

To find the kinetic energy of the electron, you actually have to use 2 different equations. Use de Broglie's to find that lambda = h/mv and solve for v. Using the v from de Broglie's equation, find the kinetic energy using E(k) = 1/2(m)(v)^2. Note that m in both these equations is the mass of an electron. Your ending units should also be in joules (kg * m^2 * s^-2).

To find the frequency of the radiation, use the E = (work function) + E(k). You have to convert the work function into joules per atom, however, since the photoelectric effect focuses on individual particles (energy is quantized). You can then relate energy to frequency using E = hv.

hv = (work function) + E(k).

### Re: Dino Nuggets Problem 8b

Posted: **Sat Nov 02, 2019 6:54 pm**

by **Amy Luu 2G**

Hello I'm having trouble understanding the next part of the problem which asks if students can see the laser pointer color. First I know you have to use the frequency of the laser to find the wavelength. Using the equation

I got 4.62 x 10^-26 m. For visible light , the wavelength falls between 400nm to 700nm. However, how do you know if the wavelength calculated, 4.62 x 10^-26 m, falls in that spectrum? I also converted to nm and got 4.62 x 10^-17 nm. Does it not fall in the range?

### Re: Dino Nuggets Problem 8b

Posted: **Mon Nov 04, 2019 5:12 pm**

by **rachel liu 3k**

ValerieChavarin3E wrote:8. B) A newly designed laser pointer with a certain frequency is pointed at a sodium at a sodium metal surface. An electron is ejected from the metal surface with wavelength 1.10nm. What is the frequency of the light from the laser pointer? The work function of sodium is 150.6 kJmol^1.

I understand that since the wavelength of the electron was given, which has mass, we would use the DeBroglie Equation. However, I am confused about how to incorporate the work function as I can't seem to cancel the proper units out.

Does someone want to help me figure out what I did wrong? Thanks!

### Re: Dino Nuggets Problem 8b

Posted: **Mon Nov 04, 2019 6:28 pm**

by **rachel liu 3k**

rachel liu 3k wrote:ValerieChavarin3E wrote:8. B) A newly designed laser pointer with a certain frequency is pointed at a sodium at a sodium metal surface. An electron is ejected from the metal surface with wavelength 1.10nm. What is the frequency of the light from the laser pointer? The work function of sodium is 150.6 kJmol^1.

I understand that since the wavelength of the electron was given, which has mass, we would use the DeBroglie Equation. However, I am confused about how to incorporate the work function as I can't seem to cancel the proper units out.

Does someone want to help me figure out what I did wrong? Thanks!

Nevermind, turns out I forgot how to do basic algebra and wasn't supposed to take out the 1/2. Thanks anyways!

### Re: Dino Nuggets Problem 8b

Posted: **Tue Nov 05, 2019 10:16 pm**

by **SajaZidan_1K**

What is our velocity for our kinetic energy?

### Re: Dino Nuggets Problem 8b

Posted: **Tue Nov 05, 2019 11:04 pm**

by **SajaZidan_1K**

I just realized you would need to calculate velocity by manipulating the equations.

### Re: Dino Nuggets Problem 8b

Posted: **Wed Nov 06, 2019 2:04 pm**

by **205150314**

rachel liu 3k wrote:rachel liu 3k wrote:ValerieChavarin3E wrote:8. B) A newly designed laser pointer with a certain frequency is pointed at a sodium at a sodium metal surface. An electron is ejected from the metal surface with wavelength 1.10nm. What is the frequency of the light from the laser pointer? The work function of sodium is 150.6 kJmol^1.

I understand that since the wavelength of the electron was given, which has mass, we would use the DeBroglie Equation. However, I am confused about how to incorporate the work function as I can't seem to cancel the proper units out.

Does someone want to help me figure out what I did wrong? Thanks!

Nevermind, turns out I forgot how to do basic algebra and wasn't supposed to take out the 1/2. Thanks anyways!

this is the wrong answer though, isnt it?

### Re: Dino Nuggets Problem 8b

Posted: **Fri Nov 15, 2019 5:35 pm**

by **rachel liu 3k**

205150314 wrote:rachel liu 3k wrote:rachel liu 3k wrote:Does someone want to help me figure out what I did wrong? Thanks!

Nevermind, turns out I forgot how to do basic algebra and wasn't supposed to take out the 1/2. Thanks anyways!

this is the wrong answer though, isnt it?

Yes, it was.