## 1B.15)

$E=hv$

Kevin Antony 2B
Posts: 61
Joined: Sat Sep 07, 2019 12:16 am

### 1B.15)

The velocity of an electron that is emitted from a metallic surface by a photon is 3.6 x 10^3 km/s. (a) What is the wavelength of the ejected electron?

I've been trying this for some time but I can't seem to get the same answer the book has. How do I tackle it?

Edit: Ok I figured it out but why do you have to use the equation lambda = h/mv and not E = .5mv^2 and then E = hc/lambda?

Katie Kyan 2K
Posts: 85
Joined: Fri Aug 09, 2019 12:16 am
Been upvoted: 1 time

### Re: 1B.15)

For part c of this problem you would use the following equation where Energy of Photon - Energy Required to Remove the Electron = 0.5mv^2 and then the equation E=hc/lambda to calculate the wavelength of the radiation that caused the photoejection of the electron. However for part a, the question is asking you to find the wavelength of the ejected electron. This means that you would just use the De Broglie equation (lambda=h/mv) since you know the velocity of the electron that was emitted to calculate the wavelength.

NRodgers_1C
Posts: 54
Joined: Thu Jul 25, 2019 12:15 am

### Re: 1B.15)

I'm stuck on part B and what equation to use. I got the wavelength of the ejected electron from part A to be= 2.0x10^-10 m. With part B asking "How much energy is required to remove the electron from the metal surface?" would we use the equation for the work function, (E= hv) - Φ = E =½ mv^2? Or do we need to use our answer from part A to help solve part B and use an equation like E= hc/λ?

805394719
Posts: 81
Joined: Wed Sep 11, 2019 12:16 am

### Re: 1B.15)

I think you cannot calculate the E = hc/lambda equation because it is defined for light. The calculations we did always assigned the speed of light to c. In that case, you could use it for calculating the energy of a photon but cannot use it for any other particle. The reason we use lambda = h/mv is that it is applicable to an electron, and therefore the wavelength can be calculated. Similarly, in class, Prof. Lavelle said that we cannot use the equations we use to find the frequency of electromagnetic radiation, for calculating the frequency of an electron. So, for example, we need to use the De Broglie equation to calculate the frequency of the light.

Maya Beal Dis 1D
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Joined: Sat Aug 17, 2019 12:16 am
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### Re: 1B.15)

What is an eV and are we required to know the conversion between that and a Joule?