How to calculate the kinetic energy, energy and frequency?  [ENDORSED]

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Chem_Mod
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How to calculate the kinetic energy, energy and frequency?

Postby Chem_Mod » Wed Apr 17, 2013 1:00 pm

Light hits a sodium metal surface and the velocity of the ejected electron is 6.61 x 105 m.s-1. The work function for sodium is 150.6 kJ.mol-1.

Answer the following three questions.
A. What is the kinetic energy of the ejected electron?
B. How much energy is required to remove an electron from one sodium atom?
C. What is the frequency of the incident light on the sodium metal surface? If you can, could you give me a step by step explanation on how to solve this?

Chem_Mod
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Re: How to calculate the kinetic energy, energy and frequenc  [ENDORSED]

Postby Chem_Mod » Wed Apr 17, 2013 1:03 pm

The steps to solve the problem are:
1. Use Ek = 1/2 mv^2 2.

2. Divide the total energy (work function) by Avogadro's number.

3. Use: kinetic energy of e- = energy of incoming photon – work function ****In addition to covering this in class, the course reader has detailed examples as does the textbook.

derek1d
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Re: How to calculate the kinetic energy, energy and frequency?

Postby derek1d » Thu Jul 06, 2017 5:20 am

Won't the mass of the electron need to be given in order to solve A) of this problem?

diegomartinez1F
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Re: How to calculate the kinetic energy, energy and frequency?

Postby diegomartinez1F » Thu Jul 06, 2017 8:46 am

Mass of electron is given:

Me= 9.10938 x 10^-31 kg

Jacinda Wollenweber 1D
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Re: How to calculate the kinetic energy, energy and frequenc

Postby Jacinda Wollenweber 1D » Tue Jul 11, 2017 12:28 am

Chem_Mod wrote:The steps to solve the problem are:
1. Use Ek = 1/2 mv^2 2.

2. Divide the total energy (work function) by Avogadro's number.

3. Use: kinetic energy of e- = energy of incoming photon – work function ****In addition to covering this in class, the course reader has detailed examples as does the textbook.


Why do we have to divide the work function by Avogrado's number? I thought the energy was given simply by adding the kinetic energy and threshold energy together.

Sarah_Wilen
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Re: How to calculate the kinetic energy, energy and frequency?

Postby Sarah_Wilen » Tue Jul 11, 2017 12:32 am

This is because the work function's energy is given in kJ/mol. You need to solve for the energy of a single unit. That was very poorly explained, sorry. Refer to this other answer:
viewtopic.php?f=14&t=21193

Kevin Morden 1E
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Re: How to calculate the kinetic energy, energy and frequency?

Postby Kevin Morden 1E » Tue Oct 10, 2017 1:57 pm

diegomartinez1F wrote:Mass of electron is given:

Me= 9.10938 x 10^-31 kg


Is the mass of an electron always going to be the same?

Chem_Mod
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Re: How to calculate the kinetic energy, energy and frequency?

Postby Chem_Mod » Tue Oct 10, 2017 2:31 pm

Yes, the mass of an electron is always going to be the same.

Sohini Halder 1G
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Re: How to calculate the kinetic energy, energy and frequency?

Postby Sohini Halder 1G » Wed Oct 11, 2017 3:42 pm

As Dr. Lavelle said in lecture, it always helps to write out the equation in words first.
For example:
Energy of incoming photon = Workfunction of metal (or energy needed to remove electron) + Kinetic energy of the electron emitted
After this, you can rearrange whatever way you need to for the problem.

Kevin Hernandez 3A
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Re: How to calculate the kinetic energy, energy and frequenc

Postby Kevin Hernandez 3A » Sat Oct 14, 2017 3:48 pm

Chem_Mod wrote:The steps to solve the problem are:
1. Use Ek = 1/2 mv^2 2.

2. Divide the total energy (work function) by Avogadro's number.

3. Use: kinetic energy of e- = energy of incoming photon – work function ****In addition to covering this in class, the course reader has detailed examples as does the textbook.


For Part c, would you subtract the work function of the sodium metal or subtract the work function of the one sodium atom?

gabbym
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Re: How to calculate the kinetic energy, energy and frequency?

Postby gabbym » Wed Oct 17, 2018 11:37 am

This was so helpful, thank you!

Ashley P 4I
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Re: How to calculate the kinetic energy, energy and frequency?

Postby Ashley P 4I » Thu Oct 25, 2018 11:24 pm

At last I finally understood what this problem was asking, thank you so much!

Liza Hayrapetyan-3K
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Re: How to calculate the kinetic energy, energy and frequency?

Postby Liza Hayrapetyan-3K » Fri Oct 26, 2018 8:37 am

Thank you so much! This was extremely helpful.

Andrew Bennecke
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Re: How to calculate the kinetic energy, energy and frequency?

Postby Andrew Bennecke » Sun Oct 28, 2018 8:43 pm

Thank you, I was genuinely confused about this topic as well!

Yiting_Gong_4L
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Re: How to calculate the kinetic energy, energy and frequency?

Postby Yiting_Gong_4L » Sun Oct 28, 2018 9:14 pm

Thank you for this explanation! This was very helpful.


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