Why we can see light and not heat?


by Physicsissuef
Tags: heat, light
Physicsissuef
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#1
Jan26-08, 06:45 AM
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Why we can see light and we can not see heat? Why can't heat be reflected?
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Hootenanny
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Jan26-08, 07:12 AM
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Quote Quote by Physicsissuef View Post
Why we can see light and we can not see heat?
By heat I assume you mean thermal radiation. If this is the case then the reason is that the photo receptors in our eyes are only sensitive to wavelengths between roughly 400nm to 700nm and thermal radiation has a wavelength greater than 700nm.
Quote Quote by Physicsissuef View Post
Why can't heat be reflected?
What makes you think it can't?
YellowTaxi
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#3
Jan27-08, 06:54 PM
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Quote Quote by Physicsissuef View Post
Why we can see light and we can not see heat? Why can't heat be reflected?
Some animals can see heat (either infra-red or ultra-violet). It's just the way our eyes are made, what we CAN see we call it visible light... I don't think there's any more to it than that. If we could see infra-red we wouldn't think it at all special, we'd just see an extra colour. Just like some electronic cameras easily detect infra-red, at no extra cost.

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Jan28-08, 07:35 AM
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Why we can see light and not heat?


Quote Quote by YellowTaxi View Post
Some animals can see heat (either infra-red or ultra-violet).
UV Heat?
DaveC426913
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Jan28-08, 08:30 AM
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Quote Quote by YellowTaxi View Post
Just like some electronic cameras easily detect infra-red, at no extra cost.
This caused a bit of a hullaballo a few years back when people realized their HandyCams were recording the naughty bits of their loved ones right through their clothes. Manufacturers hastily installed filters in their cams to prevent this. But the filters can be removed...
RonL
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Jan28-08, 09:16 AM
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We don't really see either, but rather the effects of them. What is called light, is the effect of a quantity of electromagnetic energy (photon).
Heat is a measure of energy content, that can be felt, or observed. As an example ( a section of steel is going to be cut, or tempered, with the addition of heat it goes thru visible changes, dull red- cherry red- orange- yellow- white, these colors are very dependable indicators of the temperature of the steel being heated) we see the "effect" of heat.
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Jan28-08, 09:24 AM
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Quote Quote by RonL View Post
Heat is a measure of energy content, that can be felt, or observed...
Just to make one thing clear, heat is not temperature nor is it energy. Heat is the transfer of energy from a higher temperature to lower temperature, something cannot have "heat", and to say that something "has heat" is non-nonsensical. One can think of heat as the microscopic analogy of work.
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Jan28-08, 09:37 AM
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Quote Quote by Physicsissuef View Post
Why can't heat be reflected?
If you have a space heater, look at the shiny surface behind the heating element. It's there to reflect the heat.
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Jan28-08, 10:12 AM
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Quote Quote by Hootenanny View Post
Just to make one thing clear, heat is not temperature nor is it energy. Heat is the transfer of energy from a higher temperature to lower temperature, something cannot have "heat", and to say that something "has heat" is non-nonsensical. One can think of heat as the microscopic analogy of work.
I'm confused If at 1200 degrees, i remove the flame used to bring the temperature up, how do you describe the state of the steel untill it cools to room temperature ?
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Jan28-08, 10:22 AM
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Quote Quote by RonL View Post
I'm confused If at 1200 degrees, i remove the flame used to bring the temperature up, how do you describe the state of the steel untill it cools to room temperature ?
First, the flame increases the internal energy of the steal, by transferring energy to the steel, this energy transfer is called heat as opposed to work which would be done if the steel bar were compressed. When the flame is removed, the steel bar begins to radiate energy to it's surroundings and it's temperature decreases. This thermal radiation is known as heat.

As I said previously, something does not have heat, but the energy transfered down a temperature gradient is defined as heat. In the macroscopic analogy of work, something cannot have work, but is can transfer energy by doing work.

Further reading:
http://www.physicsforums.com/showthread.php?t=169821 - an earlier thread discussing the differences between thermal energy and heat.
http://hyperphysics.phy-astr.gsu.edu...o/temper2.html
http://hyperphysics.phy-astr.gsu.edu...mo/inteng.html
RonL
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Jan28-08, 11:29 AM
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Thanks Hootenanny
Knowing something, and using the proper words, or definitions to describe what is known, is so important. Lots of study for me. Maybe the next six years will produce a marked improvment in my post. Hope were all still around that long.

Thanks for the links.

Ron


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