How much electromagnetic energy can humans sense?
Mostly in the visible light and some IR range of the EM spectrum
Our human eyes evolved to sense EM radiation in the visible light part of the spectrum as seeing in this range was critical to our survival (e.g seeing predators approaching, seeing and finding food, etc). We can also sense infrared part of the spectrum as heat, but we can't see IR with our eyes - although some technologies have been developed to do so.
We can't sense any wavelength higher than the color violet, which is why we can easily get sunburned by UV radiation that we can't sense and when you go for X-rays you feel nothing. We also can't sense EM energy lower that infrared. There is probably also a biological reason we can't sense radiation beyond UV. Radiation higher than UV is called ionizing, which means it can strip electrons from atoms and thereby breakup molecules. It would be difficult to evolve a "sense" that could detect radiation in this higher range when the radiation itself would be tearing the sensor apart! Fortunately, most of this higher energy stuff is filtered out by our atmosphere, but this becomes a real concern if you are an astronaut.
Other animals can sense different parts of the EM spectrum aside from the visible range. Some birds see in UV light and reptiles can sense IR radiation and they use this for hunting.
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Only a restricted range of frequencies—visible light, or wavelengths between about 400 and 700 nanometers—allows humans to directly detect electromagnetic energy; outside of this range, electromagnetic energy must be sensed by means of technological devices.
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When evaluating a one-sided limit, you need to be careful when a quantity is approaching zero since its sign is different depending on which way it is approaching zero from. Let us look at some examples.
When evaluating a one-sided limit, you need to be careful when a quantity is approaching zero since its sign is different depending on which way it is approaching zero from. Let us look at some examples.
When evaluating a one-sided limit, you need to be careful when a quantity is approaching zero since its sign is different depending on which way it is approaching zero from. Let us look at some examples.
When evaluating a one-sided limit, you need to be careful when a quantity is approaching zero since its sign is different depending on which way it is approaching zero from. Let us look at some examples.
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