Ask a physicist anything. (7)

[sandwiches]

Do lit up light bulbs or stars reflect light?

 

[Chalnoth]

Do lit up light bulbs or stars reflect light?

Maybe a little. But any reflected light is so far outdone by the light they emit that we wouldn't notice it.

 

[RickG]

The Sun is a black body, so its light is black body radiation, so the heat is ultimately from black body radiation

If I may suggest, you might look up what a back body actually is. The physics I studied does not describe the Sun as a black body.

 

[roach]

If this has been discussed somewhere else, I'd appreciate a link, but if not I have a question that bugs me every now and then. After looking a little harder into G. Schroeder's argument correlating cosmic time scales to the bible and understanding all the criticisms about his assumptions that make it weak, I wonder if someone could explain the physics/math a little if that's possible. If not, skool.

 

[Chalnoth]

If this has been discussed somewhere else, I'd appreciate a link, but if not I have a question that bugs me every now and then. After looking a little harder into G. Schroeder's argument correlating cosmic time scales to the bible and understanding all the criticisms about his assumptions that make it weak, I wonder if someone could explain the physics/math a little if that's possible. If not, skool.

He actually tried to do that? Huh.

Well, as far as I can tell, engaging in that sort of activity is just pure self-deception.

 

[Nabobalis]

If I may suggest, you might look up what a back body actually is. The physics I studied does not describe the Sun as a black body.

It can be described as a black body. If you have ever done a spectrum analysis of the sun light you find a nice black body spectrum of around 5600K.

 

[roach]

He actually tried to do that? Huh.

Well, as far as I can tell, engaging in that sort of activity is just pure self-deception.

hehe, i'll take that as a 'no'...
thanks anyway

 

[RickG]

It can be described as a black body. If you have ever done a spectrum analysis of the sun light you find a nice black body spectrum of around 5600K.

Its been my understanding that a black body is defined as an object that absorbs 100% of the electromagnetic spectrum, although there are no true black bodies. I understand the relationship between temperature and black body spectrum, but is that the same a black body? Just asking, I'm completely open to learning.

 

[pgp_protector]

Q: What's the best way to focus an IR Laser for soldering?

 

[Chalnoth]

It can be described as a black body. If you have ever done a spectrum analysis of the sun light you find a nice black body spectrum of around 5600K.

Well, it's a halfway-decent black body. Not all that close to a perfect one. And it's far worse within the Earth's atmosphere as a good portion of the radiation in a number of wavelengths is blocked.

The best observed black body spectrum we have is the CMB spectrum. See here:
The CMB Is A Perfect Black Body Spectrum. | The Eternal Universe

To get an idea of just how insane 400-sigma error bars are, if you have Gaussian errors, then you have about a 32% chance of falling outside of 1-sigma error bars, about a 5% chance of falling outside of 2-sigma error bars, about a 1.7% chance. To get out as far as 400 sigma, you'd have to re-run the experiment roughly 10^30,000 times.

So basically, the error bars shown on that graph are gross overestimations of the true errors. The true errors are so small that the thickness of the trend line obscures them.

 

[Nabobalis]

Its been my understanding that a black body is defined as an object that absorbs 100% of the electromagnetic spectrum, although there are no true black bodies. I understand the relationship between temperature and black body spectrum, but is that the same a black body? Just asking, I'm completely open to learning.

Yeah, the Sun isn't a true black body. However if you take a image of the Sun's spectrum and make sure you have calibrated the data correctly, you can get a reasonable estimate of the Sun's surface temperature.

 

[mzungu]

Q: What's the best way to focus an IR Laser for soldering?

Laser light does not need to be focused. In order to do soldering you will need power; So it all depends on the output power of the laser emitter. Whatever you do; WEAR EYE PROTECTION!!!!!!!

 

[Self Improvement]

Why can't I believe it's not butter?

 

[Self Improvement]

Why was Physics class an elective in high school? It seems pretty important...

 

[cupid dave]

Why was Physics class an elective in high school? It seems pretty important...

The reason is that the way Phusics is taight requires good mathe skills.

The schools need to change this, and teach a non math Pgysics or use the Truabgulation System that avoids Algebra.

 

[Chalnoth]

The reason is that the way Phusics is taight requires good mathe skills.

The schools need to change this, and teach a non math Pgysics or use the Truabgulation System that avoids Algebra.

I don't believe it is possible to teach any noticeable amount of physics without math. Students should just be expected to learn the math. That is, math should be taught earlier and better.

 

[mzungu]

The reason is that the way Phusics is taight requires good mathe skills.

The schools need to change this, and teach a non math Pgysics or use the Truabgulation System that avoids Algebra.

Yes and English should be taught without the alphabet (letters).

 

[Naraoia]

I don't believe it is possible to teach any noticeable amount of physics without math. Students should just be expected to learn the math. That is, math should be taught earlier and better.

Above all, kids should be shown that it's awesome and not all that scary.

Well, except for arithmetic. Arithmetic is positively terrifying

 

[pgp_protector]

Laser light does not need to be focused. In order to do soldering you will need power; So it all depends on the output power of the laser emitter. Whatever you do; WEAR EYE PROTECTION!!!!!!!

Strange, my laser assembly has a focus assembly for focusing the laser.

So far I can get the spot size to minimum, looking at the image through a camera, but when soldering, I'm either not getting the solder to melt, flow, or it ends up with "crystal structures?" or vaporizes the trace .

The "Manual" that came with it doesn't give any proper instructions, and support from the manufacture isn't available at this time.

We're running it at (I believe) 750mW right now max output is about 7W

 

[mzungu]

Strange, my laser assembly has a focus assembly for focusing the laser.

So far I can get the spot size to minimum, looking at the image through a camera, but when soldering, I'm either not getting the solder to melt, flow, or it ends up with "crystal structures?" or vaporizes the trace .

The "Manual" that came with it doesn't give any proper instructions, and support from the manufacture isn't available at this time.

We're running it at (I believe) 750mW right now max output is about 7W

You need more power. Unless you are soldering very small areas; It seems that thermal conduction is higher than the thermal energy you are applying on the given amount of solder. The crystals forming are an indication of a cold solder joint!

Go to maximum warp!!!!!!!!!!!!!!!!!!!