## Dino Nuggets Problem 8b

$\lambda=\frac{h}{p}$

ValerieChavarin 4F
Posts: 99
Joined: Wed Sep 18, 2019 12:18 am

### Dino Nuggets Problem 8b

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.

MingdaH 3B
Posts: 133
Joined: Thu Jul 11, 2019 12:17 am

### Re: Dino Nuggets Problem 8b

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.

ValerieChavarin 4F
Posts: 99
Joined: Wed Sep 18, 2019 12:18 am

### Re: Dino Nuggets Problem 8b

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 $E_{k}$?

alicechien_4F
Posts: 104
Joined: Sat Jul 20, 2019 12:15 am

### Re: Dino Nuggets Problem 8b

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!

Simon Dionson 4I
Posts: 107
Joined: Sat Sep 14, 2019 12:17 am

### Re: Dino Nuggets Problem 8b

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).

Amy Luu 2G
Posts: 105
Joined: Wed Sep 18, 2019 12:19 am

### Re: Dino Nuggets Problem 8b

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 $\lambda =c/\gamma$ 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?

rachel liu 3k
Posts: 56
Joined: Sat Aug 17, 2019 12:16 am

### Re: Dino Nuggets Problem 8b

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!
Attachments

rachel liu 3k
Posts: 56
Joined: Sat Aug 17, 2019 12:16 am

### Re: Dino Nuggets Problem 8b

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!

SajaZidan_1K
Posts: 56
Joined: Wed Sep 18, 2019 12:15 am

### Re: Dino Nuggets Problem 8b

What is our velocity for our kinetic energy?

SajaZidan_1K
Posts: 56
Joined: Wed Sep 18, 2019 12:15 am

### Re: Dino Nuggets Problem 8b

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

205150314
Posts: 106
Joined: Wed Feb 20, 2019 12:16 am

### Re: Dino Nuggets Problem 8b

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?

rachel liu 3k
Posts: 56
Joined: Sat Aug 17, 2019 12:16 am

### Re: Dino Nuggets Problem 8b

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.