Thermographic Gecko

Classical Mechanics Level 1

A thermographic camera creates images based on infrared radiation. Which illustration most closely resembles a real thermographic photograph taken soon (within 10 seconds) after a gecko crawls onto a human hand on a night that is in the mid 70s (~24-25°C)?

A B C

8 solutions

Danielle Scarano Staff
Mar 7, 2018

Lizards are ectotherms or "cold blooded" and therefore cannot generate their own heat. Because of this, their body temperature is influenced by their environment. On a night in the mid 70s, the lizard's body temperature will be approximately the same as its environment (without any additional sources of heat).

Unlike lizards, humans are endotherms or "warm-blooded" and can generate their own heat. The human body usually maintains an internal temperature of 98.6 °F (of 37°C). Therefore, we should expect that the human hand will be around this temperature while the lizard will be close to the temperature of the environment, as shown in choice A.

Note: If you hold the lizard longer, its body temperature will rise, eventually resulting in an image that looks like choice C.

If the lizard is held in the person's hand long enough, Won't it gain heat from their hand?

Abraham kaligambe - 3 years, 2 months ago

I was thinking the same

Leo Sjöberg - 3 years, 2 months ago

I would have preferred they Expanded on how much time had passed since the person had held the lizard, it would probably cause less confusion.

Eris Veleva - 3 years, 2 months ago

@Eris Veleva – Good point. I've specified it now, thank you.

Danielle Scarano Staff - 3 years, 2 months ago

@Danielle Scarano – I knew about lizard being cold blooded, that's why, for example, you can find them lying on the road at night. But I thought that 20 seconds is long enough human hand to warm them...

Uros Stojkovic - 3 years, 2 months ago

@Uros Stojkovic – Hmm I’m not sure, I mean we only give off a small amount of heat for such a period of time, so what I’m saying is that twenty seconds wouldn’t be enough time to get the gecko up to our own body heat, it shows to the right the colours that represent what the level of heat is, if our hand was bright yellow, the lizard wouldn’t be able to match that in twenty seconds.

I hope that makes sense 😅

Eris Veleva - 3 years, 2 months ago

@Eris Veleva – In the picture, lizard has not the exact color as human hand, it is a little bit colder, but I understand your point. The very passing of some time made me think that answer implies heat transfer. Also, because of the fact that humans generate heat and thus that temperature of the hand remains the same, I thought that warming of gecko may be possible for 20 secs. Anyway, no big deal for answering it wrong :D

Uros Stojkovic - 3 years, 2 months ago

@Danielle Scarano – Glad I could help.

Eris Veleva - 3 years, 2 months ago

indeed, then it would be C

NvmThemHereIAm . - 3 years, 2 months ago

I agree, the information given in this problem is a little misleading

Hector Rochin - 3 years, 2 months ago

Also agree the human hand is the env.

Matthew Woo - 3 years, 2 months ago

This explanation is exactly what I thought, therefore it should be C not A. The human hand has heated the gecko and 30 seconds are not long enough for it to drop back to environment temperature. Perhaps the problem's description should be less vague on how long the gecko was held.

Peter Laubender - 3 years, 2 months ago

The gecko's temperature is not dropping for 30 seconds. I believe you have misread the problem. It has been on the hand for less than 30 seconds when the photo is taken, making the correct answer A.

Danielle Scarano Staff - 3 years, 2 months ago

I read the description very carefully. It says "a human HOLDS a gecko IN their hand". It does not say that the gecko has just been ON the hand. The only assumption I made was, that the time while the gecko was held, was long enough to make the gecko's temperature change. Obviously this assumption was wrong. But the description is not clear about it.

Peter Laubender - 3 years, 2 months ago

@Peter Laubender – Dude no, it says "a gecko crawls onto a human hand". But I still agree with you, I also thought the gecko was on the persons hand for long enough to raise it's body temperature at least by some degree, I guess 20 seconds isn't long enough. Oh well, you live and you learn.

Simon The Great - 3 years, 2 months ago

@Peter Laubender – The problem states that the photograph is taken as soon as the gecko crawls into the human hand. This means the problem intends that the time is not given to the gecko to raise its body temperature.

Rohit Gupta - 3 years, 2 months ago

I noticed that you changed the description of the problem. The new description leaves no doubt about answer A being the correct one. But now my comment and the following discussion does not make sense anymore.

Peter Laubender - 3 years, 2 months ago

@Peter Laubender – Hi Peter, Yes the wording has been updated. In some cases we adjust problems to improve clarity/quality. The original wording may have been confusing to some users, so it has been adjusted. Thank you!

Danielle Scarano Staff - 3 years, 2 months ago

I clicked C but it says the correct answer is A

Led Tasso - 3 years, 2 months ago

I too faced same problem

Ram Mohith - 3 years, 2 months ago

That'y why I thought C was correct because the gecko should have been warmed up by 10 seconds...

Patrick Choi - 3 years, 2 months ago

I didn’t really read the question properly, thinking thermal conductance would come into play, having the bodies be more in equilibrium but hoping for something less extreme than C, but reading again, be that as it may, that transfer of heat simply wouldnt occur within 10 seconds and the answer then is definitely A, just explaining my thinking for those who think similarly

Patrick Bamber - 3 years, 2 months ago

Laura Gao
Mar 18, 2018

Lizards are cold blooded, which means their body temperature is the same as the environment.

Humans are warm blooded, so their body temperature is constant and around 37°C or 98°F.

If the outside temperature is lower than the human body temperature, the lizard will be colder than the human hand.

Since Lizards are cold blooded I know that the lizard's body temperature must be cold. I think I should have looked at the chart more carefully and now I understand what I did wrong. I would rate this problem a 3 because it was pretty easy to understand.

Lucia Tiberio - 3 years, 2 months ago

Philip Martin
Mar 19, 2018

We know that as geckos, a type of lizard, are influenced by their environmental heat and not by themselves. Therefore if we have a human hand around the 95 degree mark, and a gecko within 20 seconds of contact, we should expect a whiteish hand and blackish gecko. This excludes B and C.

Jeff Johnson
Mar 20, 2018

Yes. Lizard is cold blooded which is why they will look cold compared to the human hand which is at normal 98.6 body temp. I agree with everyone below. And probably everyone who posts after. Great young minds.

Yash Ghaghada
Mar 21, 2018

lizards all are cold blooded

Lillian Myhan
Mar 20, 2018

If the lizard is just now crawling onto the person’s hand the lizard would be about 70 degrees. And, if you’ve ever taken your temperature before, your hand would be about 95 degrees. Therefore your hand would be yellow, and the lizard you be purple.

Antonie Huang
Mar 20, 2018

Lizards are "cold blooded", human body is "warm blooded" therefore temperature is always stable. Between 36.5–37.5 °C (97.7–99.5 °F).

Erica Phillips
Mar 19, 2018

Gecko is a cold-blooded organism,whose body temperature fluctuates depending on the outside temperature,hence as the outside temperature is ~25-26°C. On the other hand humans are warm blooded,hence their body temperatures remain constant which is ~37°C.

Thermographic Gecko

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