Achieve HW #13 [ENDORSED]

[Chelsea Culi 3F]

The E. coli bacterium is about 2.0 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 of the photon?
What is the energy E of the electron?

I got the answer for the photon, but I'm confused on how to calculate the energy for the electron. I understand we're supposed to use E = (1/2)mv^2, but what value are we supposed to use for v?

[Antonia Valencia 2H]

Hi! We are supposed to use De Broglie's equation, λ = h/(mv) in order to determine the velocity. Indeed, we plug in the known values, such as λ (converted from micrometers to meters) as well Planck's constant and the mass of an electron, m, and use these known values to solve for the unknown value v. Once we determine v, we can plug it into E = (1/2)mv^2 to determine the energy of the electron. I hope this helps!

[Brandon Achugbue 3H]

Hi, I'm also confused on this question. I thought I knew exactly what to do, but I'm still not getting the right answer. Could anyone help me figure out what I'm missing?

(The wavelength given in mine was 1.6 micrometers)

[Tammy Shen 2L]

Hi, I'm also confused on this question. I thought I knew exactly what to do, but I'm still not getting the right answer. Could anyone help me figure out what I'm missing?

(The wavelength given in mine was 1.6 micrometers)

Hi Brandon, you should be using the E=hf or E=(hc)/wavelength equation for the first part. h is Planck's constant, c is the speed of light, and the wavelength is given so all you need to do is solve for the equation. Remember to convert micrometers to meters.

[Brandon Achugbue 3H]

Hey Tammy, I got the energy of the photon for the first part actually, but I can't find the correct kinetic energy from the electron for the second part. Since the first part of my answer is correct though, I know the wavelength is for sure 1.6 x 10^-6 m

[Kathleen Wijaya 3L]

Hey, these are the steps I did to find the kinetic energy:
1. you would have to manipulate the wavelength=h/mv equation to solve for velocity, and from there you get v=h/wavelength*mass.
2. If you plug in your wavelength, planck's constant, and mass of an electron, you should get a value for velocity that you can plug into the kinetic energy equation, E=(1/2)mv^2.
Hope this helps!

[Brandon Achugbue 3H]

Got it, thanks Kathleen! I was getting mixed up manipulating the wavelength = h / mv equation.