Sapling HW Question 25


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Nayra Gharpetian 3F
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Sapling HW Question 25

Postby Nayra Gharpetian 3F » Sun Nov 01, 2020 12:36 pm

Hi I can't figure out how to solve the second part to this problem. The problem says:

The E. coli bacterium is about 1.7 μm long. Suppose you want to study it using photons of that wavelength or electrons having that de Broglie wavelength.

What is the energy E photon of the photon?
What is the energy E electron of the electron?

I was able to calculate the energy of the photon but I don't know how to calculate the energy of the electron without being given the velocity.

Jeffrey Doeve 2I
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Re: Sapling HW Question 25

Postby Jeffrey Doeve 2I » Sun Nov 01, 2020 12:56 pm

You could solve for the energy of the electron by using its De Broglie Wavelength. Knowing the electron's wavelength would allow you to solve for velocity in the De Broglie Wavelength equation. Then, you would be able to plug the velocity of the electron into the kinetic energy formula to find the energy of the electron. Hope this helps!

Gina Spagarino 3G
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Re: Sapling HW Question 25

Postby Gina Spagarino 3G » Sun Nov 01, 2020 12:58 pm

To calculate the energy of the electron, use DeBroglie's: lambda=h/p (with lamda as the bacterial length)... and then use ((the p you solved for)/(electron mass)) as the velocity [p=mv so v=p/m]

Lea Chamoun 2J
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Re: Sapling HW Question 25

Postby Lea Chamoun 2J » Sun Nov 01, 2020 12:59 pm

The question says that the electrons have de Broglie wavelength of 1.7 μm. First, convert 1.7 μm to meters (1 μm= 10^-6m). Since λ= h/mv, then v=h/mλ. You can solve for v now because the wavelength, mass, and Planck's constant are given. Once you have found in the velocity, you can find the kinetic energy of the electron using E= 1/2mv^2

Sukhkiran Kaur 3I
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Re: Sapling HW Question 25

Postby Sukhkiran Kaur 3I » Sun Nov 01, 2020 1:06 pm

Hi! To solve this I first converted the wavelength from μm to m by multiplying 1.7 by 10^-6. Then, you can solve for v by using the equation v=h/mλ. Plug in the given mass, wavelength and Planck's constant, and then use the calculated velocity to find the KE using E=0.5mv^2.

Gian Boco 2G
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Re: Sapling HW Question 25

Postby Gian Boco 2G » Sun Nov 01, 2020 4:39 pm

You can find the velocity based because you know the wavelength and mass values. So, isolate v in wavelength = h/mv and plug it into 1/2 mv^2.

Ralph Zhang 2L
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Re: Sapling HW Question 25

Postby Ralph Zhang 2L » Sun Nov 01, 2020 4:58 pm

The key is to use electron's mass, which is given on the equation sheet, and plug that into De Broglie's equation to find the velocity.

Maddie Turk Disc 2J
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Re: Sapling HW Question 25

Postby Maddie Turk Disc 2J » Sun Nov 01, 2020 6:13 pm

Thank you so much! I think I was forgetting to convert from um to m which was throwing me off, great explanation!

Maddie Turk Disc 2J
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Re: Sapling HW Question 25

Postby Maddie Turk Disc 2J » Sun Nov 01, 2020 6:21 pm

For the equation 1/2 mv^2 is the quantity mv raised to the second power or just v?


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