## Photoelectric spectrum

$c=\lambda v$

Mary Shih 3J
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### Photoelectric spectrum

I know the textbook questions asked questions regarding which wavelength corresponds to a microwave, visible light, y rays etc. Does anyone know If we should be memorizing the entire electromagnetic spectrum?

Brennan McGurrr 3C
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Joined: Wed Sep 30, 2020 9:47 pm

### Re: Photoelectric spectrum

I don't think its necessary to memorize every single part of the spectrum. I think having an understanding of how microwaves and radio waves have a lower frequency, larger wavelength, and less energy than UV light and gamma radiation will help clarify how the spectrum works. Also how red light has a lower frequency than blue light on the visible spectrum. Hope this helps.

Aayushi Jani 3A
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Joined: Wed Sep 30, 2020 9:51 pm

### Re: Photoelectric spectrum

Yes, I agree, I don't think we have to memorize the entire spectrum but knowing the general order (which rays have a higher wavelength, what color corresponds to a lower wavelength, etc.) would definitely help while doing problems.

anikamenon2H
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### Re: Photoelectric spectrum

Like everyone else is saying a general idea of where different types of radiation fall will definitely be useful. Here's a little guide to help you!

From long to short wavelength:
radio waves --> microwaves --> infrared --> visible light --> UV --> X ray --> gamma rays
Within visible light:
It goes in order of the rainbow (red has the longest wavelength and blue/violet has the shortest wavelength)

Hope this helps!

Violet Kwan 3H
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### Re: Photoelectric spectrum

I don't think that we are required to memorize all the frequencies or wavelengths. But, it is good to remember that visible violet light is 400 nm and visible red light is 700 nm, from what I heard in a UA session and since Dr. Lavelle mentioned it in his lecture. Agreeing with the comments above, you can use this to gauge the wavelengths of the other lights in the spectrum if you know the general order.

Kiyoka Kim 3C
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### Re: Photoelectric spectrum

I agree, I think its a good idea to remember the wavelengths for visible light and have a general idea of the order of the spectrum.

John Pham 3L
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### Re: Photoelectric spectrum

Adding on to what the other comments said, it's just good to have a general idea of the order of wavelengths.

I remember the order with the mnemonic: Good Xylophones Use Very Interesting Musical Rhythms (Order of Shortest to Longest Wavelength)
- Gamma Ray, X-ray, UV, Visible, Infrared, Microwave, and Radiowaves
It's important to know that X-rays are around 0-10 picometers and Visible Light is around 400-700 nanometers

FionaHunter21
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Joined: Wed Sep 30, 2020 9:37 pm

### Re: Photoelectric spectrum

Adding on to memorizing the wavelengths, are we also supposed to know things like the frequencies or energy of each one, or can we just understand that higher frequency correlates with longer wavelength and more energy?

Katie Lam 2J
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Joined: Wed Sep 30, 2020 9:35 pm

### Re: Photoelectric spectrum

FionaHunter21 wrote:Adding on to memorizing the wavelengths, are we also supposed to know things like the frequencies or energy of each one, or can we just understand that higher frequency correlates with longer wavelength and more energy?

I don't think we have to memorize the frequencies and energies of each one. Knowing that higher frequency correlates with longer wavelength and therefore more energy is probably sufficient.

FionaHunter21
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Joined: Wed Sep 30, 2020 9:37 pm

### Re: Photoelectric spectrum

Oh wait I meant shorter wavelength, but thank you!

Massimo_Capozza_1G
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### Re: Photoelectric spectrum

Does anyone have a good video that summarises the photoelectric spectrum?

Ava Nickman
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Joined: Wed Sep 30, 2020 9:54 pm

### Re: Photoelectric spectrum

I believe we will also have access to something like this... https://www.123rf.com/photo_110493048_stock-illustration-visible-light-diagram-color-electromagnetic-spectrum-light-wave-frequency-educational-school-physics.html to help us evaluate questions such as the one on the homework
Attachments

DMaya_2G
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### Re: Photoelectric spectrum

What exactly is threshold energy? In regards to the equation that was used in lecture today for an example: E(photon) = threshold energy + Ek

clairehathaway 2J
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Joined: Wed Sep 30, 2020 9:38 pm

### Re: Photoelectric spectrum

DMaya_3C wrote:What exactly is threshold energy? In regards to the equation that was used in lecture today for an example: E(photon) = threshold energy + Ek

Hi! The threshold energy is the same thing as the work function (Φ) which essentially is the minimum amount of energy needed to remove one electron from the surface of a metal.

Morgan Gee 3B
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Joined: Wed Sep 30, 2020 9:48 pm

### Re: Photoelectric spectrum

Rather than memorizing all the different types of electromagnetic waves and their associated wavelengths and frequencies, I think it's more important to know their relative position and understand the interaction between frequency and wavelength. For example, it is good knowledge to know the approximate range of visible light (400 nm to 700 nm) and where ultraviolet waves and infrared waves are. Dr. Lavelle touched briefly on Lyman series and Balmer series which relate to ultraviolet waves and visible light so knowing the relative position would be helpful.

Gian Boco 2G
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Joined: Wed Sep 30, 2020 9:36 pm

### Re: Photoelectric spectrum

I think that it's safe to assume that we would be given an image or reference of the spectrum. But, I think it would probably be really helpful to be familiar with some of the ranges such as that of visible light.

Shalyn Kelly 3H
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### Re: Photoelectric spectrum

Hi! I definitely agree with those above that we should memorize the visible spectrum (400nm violet - 700nm red) as well as using a mnemonic to remember either shortest to longest or longest to shortest wavelengths - just remember which way you've memorized it lol.
The one I've seen that stuck with me the most is: Roman Men Invented Very Unusual X-Ray Guns (Radiowaves, Microwaves, Infrared, Visible Light, Ultraviolet, X-ray, and Gamma Rays).

Yolanda_Xing_3A
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### Re: Photoelectric spectrum

I think it’s not necessary to remember everything, but knowing the order of the spectrums is very helpful, especially visible lights.

Karina Rodriguez 2H
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### Re: Photoelectric spectrum

I doubt we'd be required to memorize the whole spectrum, but I agree with the posts above: it's probably best to have a general idea of how the spectrum is organized and its trends regarding frequencies and wavelengths.

Seraphina Joseph 1C
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### Re: Photoelectric spectrum

In a step up session I went to the instructor said we won't get to have the chart on the test, but we will need to know which order they are in.

Brian Nguyen 2I
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### Re: Photoelectric spectrum

I think it's just necessary that you know where things generally are on the spectrum. It might be helpful to keep in mind where visible light is on the spectrum (400-700 nm). You don't have to memorize the exact wavelengths, but it's necessary to know which has low and which has high frequency when solving problems.

Brandon McClelland3L
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### Re: Photoelectric spectrum

I don't think we need to memorize the exact wavelengths, I think that we just need to know the wavelengths/frequencies in relation to the different types of electromagnetic waves.

rita_debbaneh2G
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### Re: Photoelectric spectrum

I think it's a good idea to just have down them down in the order of, let's say, ascending or descending frequencies or wavelengths. In other words, don't necessarily memorize the specific numbers, but be aware of what on the photoelectric spectrum has a higher/lower frequency or wavelength with respect to other aspects of the spectrum. Maybe learning an acronym that lists the waves in ascending or descending order of a property could be a good idea.

joshtully
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### Re: Photoelectric spectrum

It could be helpful to have a general idea of what the spectrum looks like, but I do not think specifics are necessary.

Anthony_Sandoval_1D
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### Re: Photoelectric spectrum

I believe having a general idea of what the spectrum looks like should suffice so I would not worry too much about memorizing the smaller details.