37
votes
Accepted
Estimate the Sun's temperature, based on the duration of sunrise
The sunrise time gives you an estimate for the angular size of the Sun, roughly it's diameter divided by the distance to Earth.
This comes from dividing the sunrise time by 24 hours, assuming this is ...
- 128k
37
votes
How do you know mercury changes monotonically with temperature if mercury itself is used to make the thermometer?
Monotony just means that hotter always means bigger, unlike water that shrinks as you heat it from 0 °C to 4 °C. Above 4 °C it expands again. This means that about 2 °C and about 5 °C will give the ...
- 952
35
votes
Accepted
What is the minimum temperature difference which can be measured?
For a bulk substance under relatively normal conditions as you've asked about in your edited question, the "regular" standard is approximately a millikelvin (equal to 0.001 C) using platinum ...
- 1,286
34
votes
Can the temperature of a body become lower than the temperature of the surrounding air?
If conductive/convective heat transfer is low, then radiative heat loss can cool an object below the temperature of the surrounding air. As discussed in the answers to What is the temperature of the ...
- 8,270
31
votes
Accepted
What happens to matter at extreme temperatures?
As temperature rises, you break more and more bonds between particles.
Going from solid to liquid, you break a number of weak chemical bonds, leaving only strong intermolecular ones like hydrogen ...
- 6,077
31
votes
Accepted
How do you know mercury changes monotonically with temperature if mercury itself is used to make the thermometer?
This has actually been a very important problem in the history of measurement and physics more broadly. The solution was an iterative process of increasing internal consistency and precision of ...
- 526
30
votes
Why is rock or metal often cold to the touch but wood or plastic is not?
What we perceive as an object being "hot/ cold to the touch" is related to the rate at which heat is transferred from the object to your hand. In the case of touching an object with your ...
- 500
29
votes
Accepted
How do batteries lose capacity in winter?
It is true that battery performance is reduced at colder temperatures.
This is because temperature has an effect on chemical processes within the batteries, especially lithium-ion batteries, used most ...
- 29k
25
votes
What is the minimum temperature difference which can be measured?
Lately, there's a lot of buzz around a research field called quantum thermometry. The goal here is to estimate the temperature of atomic systems close to absolute zero. This means finding out the ...
- 1,158
23
votes
Accepted
Why is rock or metal often cold to the touch but wood or plastic is not?
In a room at normal room temperature, certain materials, such as
metal, glass, ceramic, or rock, will feel cold to the touch, but
others, such as wood or plastic, do not so much.
When you touch ...
- 68.8k
22
votes
How can a residential heat pump have a CoP bigger than 1?
A heat pump takes heat from outside and puts it into your house. The heat doesn't (only) come from the power that operates the pump. So it's acting like a refrigerator, but the inside of the ...
- 6,292
21
votes
How do batteries lose capacity in winter?
A deeper, physics/chemistry approach to the question:
A battery (whatever chemistry it uses) invariably contains solid electrodes and liquid electrolyte (there are batteries that have it the other way ...
- 7,598
19
votes
Accepted
The universal value of Boltzmann constant?
Boltzmann constant is the coefficient for converting temperature units to energy units. There is nothing fundamental about it.
- 57.4k
19
votes
How is the temperature of an ideal gas independent of the type of molecule?
Here is a way to think about it: put two types of ideal gases in the same box and say that initially all molecules $A$ have higher kinetic energy that molecules $B$, either because they have large ...
- 5,773
16
votes
What happens to matter at extreme temperatures?
What happens to it as we approach infinite temperature ?
Planck temperature is about $T_P = 10^{32}~\text{K}$. Wiki quotes that at this temperature :
Hypothetically, a system in thermal equilibrium ...
- 11.3k
16
votes
Interpretation of Temperature
The analogy does not break down at all, on the contrary it means exactly that: temperature is the system's internal energy per unit entropy increase while the other extensive parameters are kept ...
- 18.1k
16
votes
How do you know mercury changes monotonically with temperature if mercury itself is used to make the thermometer?
You do not know it a priori, you assume it to be true and if it leads to contradiction with other experiments and theories based on all prior experiments then you have to investigate the source of ...
- 18.1k
16
votes
What is the minimum temperature difference which can be measured?
You have a nice answer about an engineering limit (millikelvin-ish) with a link to some primary literature which I have not read. But that's an engineering answer. A more interesting answer is ...
rob♦
- 86.2k
14
votes
How is the temperature of an ideal gas independent of the type of molecule?
You are correct at saying that for a given velocity gases with different molecule masses have different pressure and temperature. That just means, that if you have two gases with different molecular ...
- 466
13
votes
How can a residential heat pump have a CoP bigger than 1?
Other answers have given the basic equations so I won't repeat them here.
The essential point is that a heat pump uses its input energy not simply to produce heat, but to TRANSFER heat out of one body ...
- 56.6k
13
votes
How do you know mercury changes monotonically with temperature if mercury itself is used to make the thermometer?
If you have no better theory of what temperature is, you define it as what your thermometer measures. That allows you to get started. Now, you can do experiments in thermal physics. If you don't see ...
- 18.6k
13
votes
Does opening both windows in a room cool the room twice as fast?
Any appreciable macroscale heat transfer in a fluid (like the air in your room) occurs through convection. A reasonable hypothesis is that the room air remains fairly stagnant with only one window ...
- 23.7k
12
votes
Can a broken chemical bond be made again?
This is exactly what chemical equilibrium teaches. Take a reaction, for example
$$
2\text{NH}_3 \leftrightharpoons \text{N}_2 + 3\text{H}_2
$$
which is endothermic. Increasing $T$ moves the ...
- 5,773
10
votes
Accepted
Why can't fire heat something hotter than itself, but electromagnetic waves can heat something indefinitely?
The First Law tells us that energy can't be lost, and the Second Law tells us that entropy can't be destroyed.
Heating transfers entropy, broadly inversely proportional to the temperature, and since a ...
- 23.7k
9
votes
Accepted
How can we explain expanding gas temperature at the microscopic level?
Pulling the piston does work on the particles. If we consider the pressure of gas as a result of particles hitting the container and being reflected back, then being scattered from a moving piston ...
- 57.4k
9
votes
How does Temperature of a system change if doing work on the environment? Can the temperature of the system increase?
I will assume that the system you are talking about is adiabatic because if it isn't we can cool or heat it to change its temperature in any desired way independently of whether the system does or ...
- 5,773
9
votes
How do batteries lose capacity in winter?
In addition to the charge in the battery itself, you also need to consider increased HVAC usage.
Unlike an internal combustion engine vehicle, which produces waste heat as a byproduct of combustion ...
- 199
9
votes
Accepted
How does adding heat cause helium-3 to freeze?
I quote from Richardson's article "The Pomeranchuk Effect":
"In 1950, I. Pomeranchuk, a well-known particle theorist, suggested that melting ³He could be cooled by squeezing it. At the ...
- 23.7k
9
votes
Can a broken chemical bond be made again?
It is certainly possible. If you heat water so that it boils into steam then you are basically supplying enough thermal energy to break the hydrogen bonds that exist between water molecules in the ...
- 47.3k
9
votes
Interpretation of Temperature
The answers saying that temperature is the energy per unit entropy are fine, but I think you must have already considered this and found it unsatisfying. Let me try to develop some intuition about ...
- 1,928
Only top scored, non community-wiki answers of a minimum length are eligible