eli5 why is the infra red part of the spectrum warm?
In: 3
Water absorbs those wavelengths very well and that’s what you’re made of. The visible spectrum is actually a gap where wavelengths of light pass through relatively easily. The ultraviolet end also gets absorbed.
The difference between the two is that IR gets the water molecule wiggling faster and increased molecular speed is what we performed as heat. UV photons carry enough energy to break chemical bonds and damage the cells but don’t speed them up by much and this don’t feel hot.
The other answers are correct but there is perhaps another aspect. Light (including infra red) has energy. If that energy gets absorbed then the object gets hot. A white object will reflect almost all the visible light but (because of physics) will absorb almost all the IR light. So to heat most objects it is more efficient to use IR light.
Everything gives off electromagnetic radiation, and the hotter the object, the higher the frequencies of light they give off.
Objects at everyday temperatures give off mostly infrared light, so anything you’d think of as warm or even hot will be radiating in infrared. After about 500 C, visible light is emitted, that is when things start to become red hot.
It is not. All light carries heat. All hot objects emit light. As an object heats up, the light it emits is of higher and higher frequencies. However, it doesn’t stop emitting lower frequencies too.
So, hot objects glow, and unless they are *very* hot the majority of the heat they emit is in the range of IR. Meanwhile, in heat lamps and the like, they use mainly IR since it is easier as well as because that much visible light would be blinding.
Radio waves also carry heat, such as seen in microwaves, but generating that much radio energy requires intent. You need to make a machine specifically to do that, whereas with IR it just happens from high temperatures.
Latest Answers