Optics B/C

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c0c05w311y
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Re: Optics B/C

Postby c0c05w311y » February 27th, 2018, 7:04 am

Consider an f/4 refracting telescope with an aperture diameter of 550mm, and an f/14 telescope.

a. which telescope would be better for taking pictures?
b. which telescope would be better for making precise observations, and why?
c. Name three typical abberations. What is a coma and how do you fix it?
d. If the eyepiece of the f/4 telescope has a focal length of 12mm, what is the magnification of the telescope? What is the angular resolution for IR light?


if i messed something up let me know

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Re: Optics B/C

Postby UTF-8 U+6211 U+662F » February 27th, 2018, 3:14 pm

Consider an f/4 refracting telescope with an aperture diameter of 550mm, and an f/14 telescope.

a. which telescope would be better for taking pictures?
b. which telescope would be better for making precise observations, and why?
c. Name three typical abberations. What is a coma and how do you fix it?
d. If the eyepiece of the f/4 telescope has a focal length of 12mm, what is the magnification of the telescope? What is the angular resolution for IR light?


if i messed something up let me know
a) If the eyepieces are the same size, the f/14 would have a bigger focal length and thus a bigger magnification and a smaller FOV, so [b]the f/4[/b].
b) [b]The f/14[/b]
c) Comatic, spherical, chromatic; A coma is a comet-like tail on a star seen through a telescope. It can be minimized by using a spherical or bestform/aplanatic lens (although spherical and chromatic aberrations are more common in refracting telescopes?).
d) 14 = focal length of objective / 550mm. M = 14 * 550mm / 12 mm = [b]642[/b] Angular resolution = 1.220 * 1 mm / 550 mm = [b]0.0022 radians[/b]

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Re: Optics B/C

Postby c0c05w311y » March 1st, 2018, 4:16 pm

Consider an f/4 refracting telescope with an aperture diameter of 550mm, and an f/14 telescope.

a. which telescope would be better for taking pictures?
b. which telescope would be better for making precise observations, and why?
c. Name three typical abberations. What is a coma and how do you fix it?
d. If the eyepiece of the f/4 telescope has a focal length of 12mm, what is the magnification of the telescope? What is the angular resolution for IR light?


if i messed something up let me know
a) If the eyepieces are the same size, the f/14 would have a bigger focal length and thus a bigger magnification and a smaller FOV, so [b]the f/4[/b].
b) [b]The f/14[/b]
c) Comatic, spherical, chromatic; A coma is a comet-like tail on a star seen through a telescope. It can be minimized by using a spherical or bestform/aplanatic lens (although spherical and chromatic aberrations are more common in refracting telescopes?).
d) 14 = focal length of objective / 550mm. M = 14 * 550mm / 12 mm = [b]642[/b] Angular resolution = 1.220 * 1 mm / 550 mm = [b]0.0022 radians[/b]

Looks pretty good! sorry ive taken so long to get back to you, I've been sick plus I had my regional competition on wednesday. The reason, according to wikipedia, that higher f numbers are better for precise measurements and such is that it is easier to reduce aberrations. Also, I wasn't really thinking about the magnification for part a but yes, if you assume the diameter is the same, there is more magnification. I was thinking about the fact that if you assume the focal length is the same, the diameter is bigger for a smaller f number, which means you get more light for pictures in a smaller amount of time.


Anyway, your turn!

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Re: Optics B/C

Postby UTF-8 U+6211 U+662F » March 1st, 2018, 7:25 pm

What is the primary difference between gamma and X rays? (Don't say wavelength/frequency/energy since there isn't a defined boundary between gamma and X rays there)

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Re: Optics B/C

Postby Tom_MS » March 2nd, 2018, 5:46 am

What is the primary difference between gamma and X rays? (Don't say wavelength/frequency/energy since there isn't a defined boundary between gamma and X rays there)
Gamma rays are produced by nuclear processes (like nuclear decay) and particle interactions (like annihilation of particle-antiparticle pairs). X-rays are produced by electrons outside of the nucleus.

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Re: Optics B/C

Postby UTF-8 U+6211 U+662F » March 2nd, 2018, 1:00 pm

What is the primary difference between gamma and X rays? (Don't say wavelength/frequency/energy since there isn't a defined boundary between gamma and X rays there)
Gamma rays are produced by nuclear processes (like nuclear decay) and particle interactions (like annihilation of particle-antiparticle pairs). X-rays are produced by electrons outside of the nucleus.
Yep, your turn!

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Re: Optics B/C

Postby Tom_MS » March 4th, 2018, 4:05 pm

What is Compton scattering? Is it elastic or inelastic? What general type of EM radiation does it affect? Describe the mechanism by which it functions.

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Re: Optics B/C

Postby c0c05w311y » March 7th, 2018, 11:37 am

What is Compton scattering? Is it elastic or inelastic? What general type of EM radiation does it affect? Describe the mechanism by which it functions.
Compton scattering is scattering of a photon from a charged particle (usually an electron) . It is inelastic: the energy of the photon is decreased after the scattering, since some of the energy goes into recoil of the electron. The electron is treated as free or loosely bound in the math for this. It primarily affects X-rays and gamma rays. With lower energy light, photons might be absorbed completely, causing the photoelectric effect, and with really high photon energy, you can get electron/positron pair production by interaction with the nucleus. Thompson scattering is basically the same thing, except the energy change of the photon is not observable because the energy of the photon is much less than the mass energy of the photon. This is why Compton scattering affects higher energy xray and gamma EMR. The important difference is that Thompson scattering can be explained with classical electromagnetism, while the existence of Compton scattering supports the quantum/particle model of light. Note that both energy and momentum are conserved.

please let me know if i made any mistakes

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Re: Optics B/C

Postby Tom_MS » March 7th, 2018, 3:58 pm

Compton scattering is scattering of a photon from a charged particle (usually an electron) . It is inelastic: the energy of the photon is decreased after the scattering, since some of the energy goes into recoil of the electron. The electron is treated as free or loosely bound in the math for this. It primarily affects X-rays and gamma rays. With lower energy light, photons might be absorbed completely, causing the photoelectric effect, and with really high photon energy, you can get electron/positron pair production by interaction with the nucleus. Thompson scattering is basically the same thing, except the energy change of the photon is not observable because the energy of the photon is much less than the mass energy of the photon. This is why Compton scattering affects higher energy xray and gamma EMR. The important difference is that Thompson scattering can be explained with classical electromagnetism, while the existence of Compton scattering supports the quantum/particle model of light. Note that both energy and momentum are conserved.

please let me know if i made any mistakes
Yep you're good (although I don't think photons have mass energy ;) ). Your turn!

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Re: Optics B/C

Postby UTF-8 U+6211 U+662F » March 14th, 2018, 6:57 pm

Restarting this... Why do light waves undergo specular reflection when hitting a mirror but diffuse reflection when hitting a piece of paper?


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