## Week 2-4 Sapling HW Quesiton 25

$E=hv$

Vivian Leung 2D
Posts: 94
Joined: Wed Sep 30, 2020 10:09 pm

### Week 2-4 Sapling HW Quesiton 25

Hi,

I had a quick question about this problem: The E. coli bacterium is about 2.4 micrometers long. Suppose you want to study it using photons of that wavelength or electrons having that de Broglie wavelength.

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

I got the answer correct but why are we not able to use E=hv to solve both questions? E=hv worked for the question about the energy of the photon but not the energy of the electron. Instead, for the energy of the electron, I had to use the de Broglie wavelength equation: E=h/p.

Xinyu Li 2I
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Joined: Wed Sep 30, 2020 9:36 pm

### Re: Week 2-4 Sapling HW Quesiton 25

From my understanding, E=hv is only used for calculating energy of photons whereas the de Broglie's equation is used for calculating energy of any moving particles with momentum.

Vivian Leung 2D
Posts: 94
Joined: Wed Sep 30, 2020 10:09 pm

### Re: Week 2-4 Sapling HW Quesiton 25

Oh ok, thank you XLi.

Thomas Vu 3A
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### Re: Week 2-4 Sapling HW Quesiton 25

Building off of the first answer, I'm pretty sure it's because with de Broglie's equation, you have to consider the mass of the particle. Photons do not have mass, I think, but electrons do so de Broglie's equation couldn't really be applied to a "mass-less" particle. Correct me if I'm wrong but I think the answer's some where on those lines.

jessicaosuna_3E
Posts: 42
Joined: Wed Sep 30, 2020 9:51 pm

### Re: Week 2-4 Sapling HW Quesiton 25

Photon does not use mass so the E=hv is only used inn that case where mass isn't part of the calculation. Additionally, when looking up the de Broglie equation, one site said it is "used to describe the wave properties of matter, specifically, the wave nature of the electron." So, with this in mind, I'm not sure if de Broglie may be specific only to electrons...? Also the E= hv equation can be used to calculate the energy required to move an electron AFTER taking into account the kinetic energy.

Vivian Leung 2D
Posts: 94
Joined: Wed Sep 30, 2020 10:09 pm

### Re: Week 2-4 Sapling HW Quesiton 25

That makes sense! Thank you Thomas and Jessicaosuna.

Chris_Butler_1A
Posts: 44
Joined: Wed Sep 30, 2020 9:32 pm

### Re: Week 2-4 Sapling HW Quesiton 25

jessicaosuna_3E wrote:Photon does not use mass so the E=hv is only used inn that case where mass isn't part of the calculation. Additionally, when looking up the de Broglie equation, one site said it is "used to describe the wave properties of matter, specifically, the wave nature of the electron." So, with this in mind, I'm not sure if de Broglie may be specific only to electrons...? Also the E= hv equation can be used to calculate the energy required to move an electron AFTER taking into account the kinetic energy.

I believe the de Broglie Equation can be applied to any particle with a mass and a velocity such as neutrons, protons, etc. because it ties into the idea that all particles act as a wave but we can only observe these kinds of activities at a smaller scale. I hope that helps!