The Law of Thermodynamics says that two bodies will eventually have equal temperatures. How is it possible that when you leave your car in the sun, it gets hotter in the car than it is outside? Why isn’t the car at the same temperature as the outside, as it should be according to the Law?
Thermodynamics – How Can It Get Hotter Inside a Car Than Outside?
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There is a nice article about this on the Scientific American web site. The simple answer is that we don't know why the corona is so hot though there are a few well established and plausible suggestions.
Some introduction:
The coronal temperature is not just a bit higher than the Sun's surface, it's getting on for a thousand times hotter - a few million kelvin as opposed to around $5,700$ K at the surface of the Sun. But what we mean by this is the atoms/ions in the corona have very high velocities. The corona is pretty tenuous. The pressure in the corona is around a million times lower than the pressure at the Earth's surface, so the corona is pretty close to a vacuum. Rather than thinking of the corona as a hot gas we should think of it as a region in which a low density of atoms/ions have been accelerated to high velocities. The question is then what is doing the accelerating?
An obvious suggestion is that the Sun's magnetic field is responsible for transferring energy to the corona. The magnetic field is subject to various forms of turbulence and since the ions in the corona interact strongly with the magnetic field it is quite plausible that turbulence in the field is accelerating the ions.
The other suggestion is that turbulence at the surface generates sound waves, in effect the sort of shock waves created by explosions on Earth, and it's these shock waves that transfer energy to the particles in the corona.
But right now we don't have the experimental data to tell which, if either, of these mechanisms is correct.
1) I think both objects would absorb radiation from the sun and their temperatures would increase until they reach their final temperatures.
A (perfect) white body, by definition, reflects all incident radiation and thus would not absorb any radiation from the sun.
2) The final temperature for the white object is lower than for the black object.
If only considering radiative heating, yes. The white body will not heat up at all (see also 5).
3) The white object will take longer than the black object to reach its final temperature.
No, see 2.
4) The black object behaves like a blackbody. Blackbodies are said to be perfect emitters and perfect absorbers. But even a white object reflects (in theory) all the incident energy. So what is the difference? That reflection does not contribute to raising the T of the object?
They will produce different spectra. The white body reflects all the incident radiation, so it's spectrum will be the same as that of the incoming sunlight. The black body, however, absorbs all incoming sunlight and emits blackbody radiation.
5) In some cases, two different objects, left in the same room, reach the same temperature as the room. Why doesn't that happen when the same two object are left under the sun? What if they were left in the shadow? Would they eventually have the same temperature?
In general, there are more ways for heat transfer to occur than through radiation. Two other ways are conduction and convection. These are the main mechanisms by which objects reach thermal equilibrium with their surroundings. If you were to place two objects outside in the shadow, they would both eventually reach thermal equilibrium with the air (mainly through conduction and convection).
Best Answer
That is not an absolute Law. There are conditions, and one of those conditions involves the energy input to the bodies. If this Law was absolute, then the Sun would be at the same temperature as the universe, about 2.7 K, because the universe is much larger than the Sun. But the Sun has an internal energy converter/source which raises its local temperature.
The interior of a closed car in the sunlight will be higher because of a greenhouse effect. The glass of the car is transparent to the visible light, so that energy is absorbed by the interior of the car (the seats, dashboard, and floor) increasing their temperature. Those items then emit infrared radiation and the glass is fairly opaque to that radiation and the energy stays in the car. So more energy comes in the glass than is escaping out of the glass.
Because the trunk/boot doesn't have a glass opening to let radiation in, it will generally stay quite a bit cooler than the passenger compartment. Whatever radiation the trunk lid gets is reflected and radiated back out fairly efficiently. That's not to say it doesn't get hot, but it doesn't get to the same as the passenger compartment.