You feel the heat under the Sun. Sunlight carry heat, right? Photon is massless, how does it carry heat energy with it to travel so far?
Correct Wrong Correct It doesn't Have you tried Wikipedia? Please Register or Log in to view the hidden image!
A photon carries electromagnetic energy, according to Planck's relation, E = hν, in which E is energy, h is Planck's constant and ν is the frequency of the radiation. So the higher the frequency the more energy each photon carries. Photons with frequencies in the range 3GHz-30THz, corresponding to wavelengths in the range 10cm-10μ, are of the right energy to excite rotations and vibrations of molecules. Rotations and vibrations of molecules, along with translational motion of the whole molecule, involve molecular kinetic energy, which corresponds to heat. More energetic photons, in the visible region, excite electrons from the ground state to excited states. These excited states can lose energy again either by re-radiating another photon or via more complicated processes*, involving vibration and collision of molecules, which convert the energy of the electronic excited states to vibrational, rotational and translational kinetic energy, i.e. to heat. In summary, photons carry energy which, when it is absorbed, heats up the object that absorbs it. *This is actually a rather complicated and interesting field of physical chemistry, known as photochemistry, which was the speciality of my tutor at university.Please Register or Log in to view the hidden image!
planets farther away from Sun is cooler, what cause the heat to lose on its way of travel? can we measure photon kinetic energy? 1/2 mv^2?
The total energy per sec reaching Jupiter's orbital distance is no less than that reaching Earth's orbital distance. However, it is spread out over a spherical surface some 25 times larger. Thus the energy/sec per square meter is less at Jupiter's orbit because that square meter intercepts a smaller fraction of the total energy per sec emitted by the Sun than a square meter of surface at Earth orbit distance does.
To add to what Janus has explained, the energy of each photon is the same, but there are fewer photons per unit area, or volume of space, because they are radiating, i.e. moving radially outward, as they move away from the sun. Obviously you cannot apply 1/2 mv² to a photon, since it has no mass (m=0). I gave you the correct formula for the energy in post 4.
Side question: I read that photon can not escape black hole. When a photon is trapped into a black hole, will it increase its speed? But theory of relativity says speed of light is constant.
You understand that every mass has an escape velocity? The EH of a BH has an escape velocity of 300,000kms/sec [186,000 m/p/second] Since that is the constant speed of light, it does not escape. When a photon is inside a BH, the spacetime curvature is such that escape velocity exceeds "c", therefor the unlucky photon is taken for a ride to the center/singularity of the BH.
This may be of interest Speculative Sunday: Can a Black Hole Explode? Please Register or Log in to view the hidden image! Figure 1. The Supernova Remnant Cassiopeia A, all that remains of a star that ran out of fuel. It contains either a neutron star or a black hole… could that black hole someday explode? (Image created using data from the Hubble, Spitzer, and Chandra space telescopes.) A Big Bang......? http://www.thephysicsmill.com/2015/06/14/speculative-sunday-can-a-black-hole-explode/
Question: Is energy infinitely compressible? If not, at what threshold density does the equation inside a BH trigger a mega-quantum event where collapse s reversed and a mega-quantum energetic expansion results in a Big Bang where all sequestered energy is released as a white hole, creating a new universe in an act of self similar procreation. Making copies of itself. A natural way of universal 3D printing.......Please Register or Log in to view the hidden image!
I learn that heat can be transmitted by conduction, convection and radiation. So, the heat radiation from the Sun does not really need photon to play a role, right?
It has already been explained to you about light/photons having a duel nature. Heat is radiated through space as waves.
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Yeah I sometimes answer these regardless, if I think another innocent reader might wonder what the answer is. But that doesn't apply to this one.
heat is kinetic energy of the body's atoms , if it is solid, it is vibrational energy. a black body can radiate heat,but there is no light
OK, since Michael has given this a like, there may be a point in disentangling it. First, the sun is a pretty good example of a black body. A "black body" in physics does not mean something emitting no visible light. "Black" is used to denote the property of being a perfect emitter and absorber of radiation, with no reflection from the surface. A "black body" is thus the opposite of a perfectly reflecting body, rather than the opposite of a "white" body. Second, any body at a temperature above absolute zero will emit electromagnetic radiation. Whether you call it "light" or "heat" does not matter. It is just EM radiation. People sometimes use the term heat as shorthand for radiation in the frequency range I indicated in post 4, that excites vibration and rotations in molecules of matter.
No. People often confuse the words "heat" and "temperature", and what you just said is evidence of that confusion. Black body radiation is electromagnetic, which includes light. The Sun is approximately a black body radiator, and you'll have noticed it produces some light.
I have a new wooden spoon Thought would try it out Sorry Please Register or Log in to view the hidden image! Please Register or Log in to view the hidden image!
