Confused About The Colour of Spacesuits and Bedouin Garb

[Hexon]

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questions come from EK Gen Chem Q's 316-321 which basically cover thermodynamics.

Now i understand that a blackbody radiator is the ideal radiator that absorbs and transmits heat energy/radiation perfectly, yet it doesn't reflect it so what's the difference between absorbing and transmitting and simply reflecting? they appear to be quite similar on the atomic level right? radiation either in particle or wave form would have to reflected back out of a hypothetical blackbody radiator right?

Now about the berbers/tusken sand raiders;
Q319:
Indigeneous inhabitants of desert regions often wear loos black robes instead of white robes. Which best explains why?

a) black robes stay cooler in the sun.
b) black robes don't emit as much radiation and thus keep the wearer cool
c) white robes reflect the heat into the wearer whereas black robes do not.
d) black robes warm the air between the robe and the skin causing it to rise. The wearer is cooled by convection.

the answer was d), which confused me; surely white surfaces reflect light and radiation whilst black surfaces absorb both right?

Q321 was similar:

Why are Astronauts' spacesuits white?

a) in the cold dark of space, white reflects more than black.
b) in the cold dark of space, white doesn't radiate as much as black
c) in the warm sunshine, white absorbs more than black
d) in the warm sunshine, white doesn't radiate as much as black.

answer was b)

so what the heck is the difference between white and black when it comes to radiation and heat absorbance or reflection? these questions have made me doubt what i used to learn in high school which was that dark generally absorbs heat whilst white reflects heat.

 

[Isoprop]

For the MCAT, you should know that reflection means that the energy never really "hit" the material or body. In other words, for a perfectly reflective material, I can never increase the temperature by only radiation. For a black body, I can increase the temperature by using only radiation because the black body will absorb the energy. It can then release that energy through emission.

For the first question, I believe you are right in that c and d are potentially both correct answers, but d is the better answer because convection cooling is faster than radiation.

For the second question:
a is wrong for 2 reasons. In the cold, dark space, there is no radiation. So there is no reflecting to be done. But even if there were reflection, that would make the astronauts even cooler, which doesn't help.
c is wrong because black absorbs more than white.
d is true but doesn't help the astronauts because we want more radiation to dissipate the heat in sunlight.

So b is the best answer. Another good answer would have been, "in the warm sunshine, white suits REFLECTS more than black."

 

[Hexon]

For the MCAT, you should know that reflection means that the energy never really "hit" the material or body. In other words, for a perfectly reflective material, I can never increase the temperature by only radiation. For a black body, I can increase the temperature by using only radiation because the black body will absorb the energy. It can then release that energy through emission.

For the first question, I believe you are right in that c and d are potentially both correct answers, but d is the better answer because convection cooling is faster than radiation.

For the second question:
a is wrong for 2 reasons. In the cold, dark space, there is no radiation. So there is no reflecting to be done. But even if there were reflection, that would make the astronauts even cooler, which doesn't help.
c is wrong because black absorbs more than white.
d is true but doesn't help the astronauts because we want more radiation to dissipate the heat in sunlight.

So b is the best answer. Another good answer would have been, "in the warm sunshine, white suits REFLECTS more than black."

beautiful explanation, thank you for that🙂

so reflection means nothing has been absorbed, therefore no temperature rise😛
and astronauts' suits are white to reflect radiation but suppose astronauts are in the dark area of space where there is no sunlight; would they be negatively impacted in any way?

 

[MT Headed]

suppose astronauts are in the dark area of space where there is no sunlight; would they be negatively impacted in any way?

No, because their suits are white.

A black suit would permit the easy flow of heat from a hot body (astronaut) to a cold body (outer space). This would be a problem.

A white suit reflects, and thus prevents the flow of heat. In the shadows, it prevents the astronaut from losing heat. In bright sunlight, it prevents the absorption of heat into the astronaut from the sun.

It turns out that actual space suits are incredibly insulating. The biggest problem a space suit has is that it doesn't dissipate the body heat generated by the person inside. Those huge built-in back packs on space walk suits are mostly air conditioning units!

 

[Hexon]

No, because their suits are white.

A black suit would permit the easy flow of heat from a hot body (astronaut) to a cold body (outer space). This would be a problem.

A white suit reflects, and thus prevents the flow of heat. In the shadows, it prevents the astronaut from losing heat. In bright sunlight, it prevents the absorption of heat into the astronaut from the sun.

It turns out that actual space suits are incredibly insulating. The biggest problem a space suit has is that it doesn't dissipate the body heat generated by the person inside. Those huge built-in back packs on space walk suits are mostly air conditioning units!

thanks for that, MT Headed🙂

 

[dmf2682]

How would the problem change if you had a suit with black on the inside and white on the outside? Vice versa?