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
29
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 ...
- 506
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 ...
- 17.1k
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 ...
- 17.5k
7
votes
Accepted
Solving the heat equation around a point of constant temperature
The temperature held at one point in a otherwise uniform temperature field within a medium does not have enough oomph to propagate into the medium. Consider the steady state solution for a tiny ...
- 32.2k
3
votes
Accepted
Temperature coefficient for avalanche breakdown
In an avalanche breakdown minority carrier electrons are accelerated by the applied electric field and their kinetic energy increases until it becomes large enough to excite an electron from the ...
- 349k
2
votes
Temperature in a locked room with a fan
In fact, evaporation does not merely make you "feel cool", it actually does cool YOU. A fan blowing on a PERSON cools the PERSON (through evaporative cooling) but adds heat to the ROOM. Fans ...
- 21
2
votes
Temperature integrations
Yes, you can integrate a temperature field $T(x,y,z,t)$ over all variables the same way you could integrate any other function. However, that does not mean that said integral must have a direct ...
- 1,535
2
votes
Accepted
Can something become hot enough that it stops glowing?
According to Wien's displacement law,
for rising temperatures the maximum of emitted radiation
shifts from infrared to visible, ultaviolet, X-rays, ...
But the maximum of perceived light shifts
from ...
- 35k
2
votes
What happens to entropy and energy when you inject heat into 2 systems in thermal equilibrium?
If all other properties of the two systems and the combined system are the same, and only the temperature increases, why would they leave the curve? Only the slope will decrease with increasing T. The ...
- 33
2
votes
Accepted
Weird derivative with respect to inverse temperature identity in Tong's statistical physics lecture notes
...I came across this weird identity...
$$
\frac{\partial}{\partial \beta} = -k_B T^2 \frac{\partial}{\partial T}
$$
This is just the chain rule of differentiation.
whereas $ \beta $ is as usual $ \...
- 15.6k
1
vote
Accepted
Gibbs Free Energy change under non-constant temperature
The Gibbs energy is useful in analyzing processes under the condition that $T$, $P$ and $N_i$ is constant (in the case of reactions $N_i$ refers to atoms, not molecules). Reactions, exothermic or ...
- 5,708
1
vote
What happens to entropy and energy when you inject heat into 2 systems in thermal equilibrium?
You have not specified so but let us assume that the two parts, $A$ and $B$, after the injection of the thermal energy into $A$, are isolated together and their only interaction is with each other via ...
- 17.1k
1
vote
Can a propagating sound wave change the temperature of the medium?
For sound travelling in a gas the changes which occur can be assumed to be approximately adiabatic.
You might have noticed that the speed of sound $c = \sqrt{\frac{\gamma P}{\rho}}$ where $P$ is the ...
- 91.8k
1
vote
Can a propagating sound wave change the temperature of the medium?
The amount of pressure rise caused by the passage of a sound wave is very small compared to ambient, which by the gas law means the temperature rise will be correspondingly small. Note also that the ...
- 88.1k
1
vote
Would an object moving close to the speed of light appear colder to a stationary observer?
But this doesn't seem to be right, since the properties electromagnetic waves should be the same in both reference frames.
You are right about everything. Except for that quote. So that must be the ...
- 1,871
1
vote
How do you know mercury changes monotonically with temperature if mercury itself is used to make the thermometer?
Monotonicity is easy to observe. Hazard a guess, time might be involved to get linearity. A flame isn't the most stable source of heat, but could possibly boil water in a consistent amount of time. ...
- 2,412
1
vote
Is it possible that a battery goes flat faster in a cold environment?
A simple way to look at this is to realize that a battery relies on chemical reactions to produce electrical power, and this will naturally yield in a first approximation an exponential dependency of ...
- 88.1k
1
vote
Is it possible that a battery goes flat faster in a cold environment?
While it is relevant that the internal resistance of a battery increases when the temperature decreases, and thus the device wastes more energy, I don't think this is the main thing happening. The ...
- 5,971
1
vote
Using $S$ and $T$ to parameterize thermodynamic state
After thinking about this I have come to the conclusion that the TA was probably just making a mistake. His goal was to argue that
$$\left( \frac{\partial M}{\partial H} \right)_T = \left( \frac{\...
- 969
1
vote
Using $S$ and $T$ to parameterize thermodynamic state
You have already pointed out in Eq. (5) that $(S,V) \mapsto (T,V)$ is a bijection, now if you also assume that this bijection is a smooth one then you should be able to substitute in $dU=TdS-pdV$ ...
- 17.1k
1
vote
Measurement that takes into account air density and average kinetic energy?
Heat flows from high temperature to low temperature objects. So if the average kinetic energy is high and hence the low-pressure air temperature is hotter than something else, there will still be a ...
- 30.2k
1
vote
Accepted
Is kilo-Kelvin ($\rm kK$) avoided as it would be confusing?
In certain fields there are "customary" ways of managing unit multipliers. For thousands of kelvins, they are expressed as four-digit or 5-digit numbers. Similarly, for measurements of small ...
- 88.1k
Only top scored, non community-wiki answers of a minimum length are eligible