Optics B/C

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Re: Optics B/C

Post by cngu23 » January 11th, 2012, 5:01 am

cngu23 wrote:What are some good sources for information on telescopes, cameras, and microscopes?
Right now, I'm using the Giancoli physics textbook and wikipedia.
On the Ichaelm's practice test 2011, the answer for the question "Dd photons ever have zero mass?" is no. But aren't photons massless, and they only have momentum?
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Re: Optics B/C

Post by Schrodingerscat » January 11th, 2012, 6:12 am

I believe that their rest mass is zero, but they exist constantly moving, which gives them energy and therefore mass.

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Re: Optics B/C

Post by foreverphysics » January 11th, 2012, 10:08 am

Schrodingerscat wrote:I believe that their rest mass is zero, but they exist constantly moving, which gives them energy and therefore mass.
That can also be debated by neutrinos, but essentially, that's what it is.
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Re: Optics B/C

Post by SciBomb97 » January 11th, 2012, 12:35 pm

Let's just go with Schrodingerscat's answer.
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Re: Optics B/C

Post by foreverphysics » January 11th, 2012, 12:39 pm

SciBomb97 wrote:Let's just go with Schrodingerscat's answer.
But...but...it's all debatable! And if it's debatable, then...
Oh yeah, and Higgs Bosons are an exception.
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Re: Optics B/C

Post by Paradox21 » January 15th, 2012, 8:53 pm

Just because a particle has energy, that does not mean it has mass. A photon could collide with another particle and have its energy converted into mass, but the photon itself is massless. Einstein's relativity shows that any object with mass can never travel at the speed of light, therefore a photon traveling at the speed of light necessarily could never have mass!. Neutrinos have a very very small, non-zero mass. This means that in theory, they will never be able to travel at the speed of light, or faster than the speed of light. Recently there has been much ado about scientific research finding neutrinos that go faster than the speed of light. In general, the physics community thinks that there must be some flaw in the experiment (last I heard, they were considering time dilation due to changes in gravitational field, as dictated by General Relativity).

Considering particles to change mass because they are moving leads you into some murky scientific waters. One of the fundamental underpinnings of Relativity is that no reference frame is better than another one. This means that considering a particle emitted from a space craft is equally valid if you do it from a reference frame of an observatory on Earth, or in a reference frame that is traveling with the same speed and direction as the particle. Consider a particle with a rest mass of 0. In one reference frame, the particle is moving, in the other, the particle is at rest! This would result in a particle having a quantifiable finite mass while simultaneously having zero mass, a contradiction! For this reason, it is correct to always consider a photon to have zero mass. You can add energy to a photon to increase its momentum, but you can never add energy to increase the mass of a photon.
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Re: Optics B/C

Post by SciBomb97 » January 16th, 2012, 6:55 am

Paradox21 wrote:Just because a particle has energy, that does not mean it has mass. A photon could collide with another particle and have its energy converted into mass, but the photon itself is massless. Einstein's relativity shows that any object with mass can never travel at the speed of light, therefore a photon traveling at the speed of light necessarily could never have mass!. Neutrinos have a very very small, non-zero mass. This means that in theory, they will never be able to travel at the speed of light, or faster than the speed of light. Recently there has been much ado about scientific research finding neutrinos that go faster than the speed of light. In general, the physics community thinks that there must be some flaw in the experiment (last I heard, they were considering time dilation due to changes in gravitational field, as dictated by General Relativity).

Considering particles to change mass because they are moving leads you into some murky scientific waters. One of the fundamental underpinnings of Relativity is that no reference frame is better than another one. This means that considering a particle emitted from a space craft is equally valid if you do it from a reference frame of an observatory on Earth, or in a reference frame that is traveling with the same speed and direction as the particle. Consider a particle with a rest mass of 0. In one reference frame, the particle is moving, in the other, the particle is at rest! This would result in a particle having a quantifiable finite mass while simultaneously having zero mass, a contradiction! For this reason, it is correct to always consider a photon to have zero mass. You can add energy to a photon to increase its momentum, but you can never add energy to increase the mass of a photon.
You take college physics, don't you?
Well now things are (kinda?) starting to make sense, except this is physics we're talking about, so I guess it will never actually make sense, we just have to pretend it does.
Then Ichaelm's practice test for 2011 was wrong after all, just proving how hard physics actually is... :geek:
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Re: Optics B/C

Post by foreverphysics » January 16th, 2012, 7:06 am

SciBomb97 wrote:
Paradox21 wrote:Just because a particle has energy, that does not mean it has mass. A photon could collide with another particle and have its energy converted into mass, but the photon itself is massless. Einstein's relativity shows that any object with mass can never travel at the speed of light, therefore a photon traveling at the speed of light necessarily could never have mass!. Neutrinos have a very very small, non-zero mass. This means that in theory, they will never be able to travel at the speed of light, or faster than the speed of light. Recently there has been much ado about scientific research finding neutrinos that go faster than the speed of light. In general, the physics community thinks that there must be some flaw in the experiment (last I heard, they were considering time dilation due to changes in gravitational field, as dictated by General Relativity).

Considering particles to change mass because they are moving leads you into some murky scientific waters. One of the fundamental underpinnings of Relativity is that no reference frame is better than another one. This means that considering a particle emitted from a space craft is equally valid if you do it from a reference frame of an observatory on Earth, or in a reference frame that is traveling with the same speed and direction as the particle. Consider a particle with a rest mass of 0. In one reference frame, the particle is moving, in the other, the particle is at rest! This would result in a particle having a quantifiable finite mass while simultaneously having zero mass, a contradiction! For this reason, it is correct to always consider a photon to have zero mass. You can add energy to a photon to increase its momentum, but you can never add energy to increase the mass of a photon.
You take college physics, don't you?
Well now things are (kinda?) starting to make sense, except this is physics we're talking about, so I guess it will never actually make sense, we just have to pretend it does.
Then Ichaelm's practice test for 2011 was wrong after all, just proving how hard physics actually is... :geek:
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And to bring the topic back to Optics, does anyone have any idea how to modify hangfromthefloor's laser shoot template for 5 mirrors?
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Re: Optics B/C

Post by SciBomb97 » January 22nd, 2012, 3:51 pm

In the laser shoot, is the laser on from the beginning and just the mirrors are covered, or are both the laser and the mirrors covered?
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Re: Optics B/C

Post by Gillen » January 22nd, 2012, 4:06 pm

SciBomb97 wrote:In the laser shoot, is the laser on from the beginning and just the mirrors are covered, or are both the laser and the mirrors covered?
The laser is normally off and all the mirrors are covered, based on what I've seen.

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