Sapling homework Question 9

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Jaclyn Dang 3B
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Joined: Wed Sep 30, 2020 10:02 pm

Sapling homework Question 9

Postby Jaclyn Dang 3B » Mon Oct 19, 2020 5:18 pm

Hi, I'm not sure where to start on this problem, if anybody can give me the steps along with a quick reasoning/explanation, it'd be highly appreciated!

As you may well know, placing metal objects inside a microwave oven can generate sparks. Two of your friends are arguing over the cause of the sparking, with one stating that the microwaves "herd" electrons into "pointy" areas of the metal object, from which the electrons jump from one part of the object to another. The other friend says that the sparks are caused by the photoelectric effect. Prove or disprove the latter idea using basic physics.

Suppose the typical work function of the metal is roughly 4.260×10−19 J. Calculate the maximum wavelength in angstroms of the radiation that will eject electrons from the metal.


Thank you!

Posts: 78
Joined: Wed Sep 30, 2020 9:39 pm

Re: Sapling homework Question 9

Postby darchen3G » Mon Oct 19, 2020 5:26 pm

E = hc/lambda

In your case, 4.26*10^-19 = hc/lambda then solve for lambda.

For the second part of the question, use E=hf to see if it has enough energy.

Jenny Lee 2L
Posts: 69
Joined: Thu Oct 08, 2020 12:15 am

Re: Sapling homework Question 9

Postby Jenny Lee 2L » Mon Oct 19, 2020 6:52 pm

Hi Jaclyn!

Here is the formula that was used for the photoelectric effect: (E per photon) = (Work Function) + (KE)

The work function is the bare minimum you need to eject the electron from the metal surface with 0 kinetic energy. By maximum wavelength, it's asking us for the wavelength needed to match the energy of the work function (because E = Work Function if KE=0).

So we do:
1. Work function = E = 4.620x 10^-19 J
2. E= hv, find v (frequency)
3. Use c= (lambda)(v) to find the wavelength

Hope this helps!

Brianna Martilla 1C
Posts: 73
Joined: Wed Sep 30, 2020 9:58 pm

Re: Sapling homework Question 9

Postby Brianna Martilla 1C » Mon Oct 19, 2020 11:25 pm

Whenever I am given a problem I always see what is given and what I am being asked to find. We are given the value for energy and we are asked to find the wavelength. We can use E=hc/lambda, rewrite that as lambda=hc/E, then solve for lambda because h and c are constants. Just make sure to convert your answer to angstroms (1 angstrom=10^-10 m) because the answer is in meters.

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