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5

An object at 1000K glows red because that is basically dominating the radiation that it is emitting that we can see. Most of the radiation it emits emerges in the infrared part of the spectrum to which our eyes are not sensitive. Your edited question asks about the appearance of hot metals. The chart below is an example of a "colour-temperature" chart for ...


5

Practically speaking, diamond has the highest thermal conductivity of any "reasonable" material, about 5 times greater than copper. Additionally, its specific heat is about 30% greater than copper or brass, but about 10% that of water. As a result, a diamond will heat up faster than just about anything else, particularly when immersed in a liquid like water ...


4

Are spectra (both fluorescence and absorbance) of any molecule dependent on temperature? The characteristic wavelengths do not change with temperature but the intensities will. As temperature changes, the relative concentrations of molecules with particular energy levels will change and that will affect the relative strength of absorption bands and the ...


4

Yes you are right. You end up having a varying electric field which generates a varying magnetic field which in turn generates an electric field etc... This causes a particular type of radiation called black body radiation.


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The frequency of the first harmonic oscillation is the higher the higher the tension in the string. As temperature increases, the length of the string slightly increases. The change of linear mass density is thus negligible, but the corresponding change of tension in the string is not. The tension decreases and thus the speed of waves and frequency of ...


3

To a good approximation the radiation emitted from a hot piece of steel will be the same as emitted by a black body. The relationship between the wavelength $\lambda$ of light emitted by a black body and the temperature $T$ is given by Planck's law: $$ B = \frac{2hc^2}{\lambda^5} \frac{1}{e^{hc/\lambda k_b T} - 1} $$ where $B$ is the spectral radiance, $h$ ...


3

Yes this does really help. Due to the density anomaly of water it expands even when it's frozen and in a solid state (ice). This causes your pipes to burst over the time due to the increased pressure. Letting the water dripping a little bit serves as a pressure relief and therefore prevents the pipes from bursting. It is important to run both, hot and cold ...


2

Note that to figure out how quickly an object heats up, you need the ratio of two quantities - the thermal conductivity, and the volumetric heat capacity. If the former is large AND the latter is small, you get an object that will quickly take up the heat of its surroundings. This parameter is known as the "thermal diffusivity" $$\alpha = \frac{k}{\rho ...


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You've got your work cut out for you, so this answer can only point you in a direction. This calculation can be difficult because there is a profusion of pieces of terminology with subtly different meanings. Find a book/other source (but for the straight dope I suggest a book) which discusses radiometry and the differences between radiant flux, radiance, ...


2

"Thermal energy" is a bit of a misnomer because "thermal" really refers to a method of energy transfer, not energy storage. When energy moves from one system to another, it can do so via a thermal process (e.g. conduction, convection, radiation) or a mechanical process (something pushes on something else). So technically, I wouldn't call $\frac{3}{2}kT$ the ...


2

I looked up the vapour pressuer of carbon dioxide at room temp (20 deg. C) and it is 57 bar, so I don't think you can have seen a cylinder of CO2 at 250 bar. If it is advertised as containing '250 bar' then the reality will be a lower pressure plus some solid CO2 in the bottle as well. For nitrogen, commercial cylinders can be supplied up to about 200 or ...


1

At research laboratories where liquid nitrogen (and oxygen) are commonly used every day, closed containers of LN and LOx are routinely transferred and stored. These pressurized tanks typically operate at around 20 atmospheres and hold between 50 and 250 liters. For short-term needs and operations, the LN will be transferred to a vented vacuum-jacketed ...


1

Start by assessing the relative importance of each $Q$ term. Assume some order of magnitude values for the unknowns (based on experience and/or intuition) and see how big $Q_{lin}$ is compared to e.g. $Q_s$. Do that for all $Q$ terms and hope some will be negligible so they can be discarded. My guess is that $Q_{lin}$ and $Q_e$ are insignificant. You are ...


1

Water, like most liquids does indeed get more viscous as its temperature approaches freezing point. See the graph below, which I took from the "Engineering Toolbox" However, what's interesting about this curve is that it does not diverge as $T\to 0^\circ{\rm C}$. The reason is that a phase change really is for all effective purposes a discontinuous ...


1

Force due to pressure over a given area is $F=AP$. A bubble will have three forces to consider. 1. Air pressure from air inside the bubble pushing the wall of the bubble outward (trying to make the bubble bigger) 2. Air pressure from air outside the bubble pushing the wall of the bubble inward (trying to make the bubble smaller), and 3. a surface tension of ...


1

If you measure that it takes an apple 2 days to rot, then you note that another apple (which happens to be colder) takes 3 days to rot, you could either conclude that time has slowed down, or that the rotting of an apple does not make a very reliable clock. I conclude the latter. A cold apple and a hot apple are both experiencing the same passage of ...


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If the room is isolated (can't exchange heat with the rest of the universe) then the air conditioner must be "part of the room" and only able to draw in air from the room and expel air to the room. Also, the power source for the air conditioner and fan must be inside the room, otherwise the system isn't isolated. So let's say we have a battery to operate ...


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I am unsure of the solution below because of my free manipulation of P and Q, so if anyone has a comment or better way, let me know. Some assumptions: I assume that in the question you meant that we have a body with a surface area $A$, which is at an initial temperature $T_{0}$ and is losing energy by means of radiation, for which you used the ...


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Resistance changes with temperature The temperature coefficient of resistance, or TCR, is one of the main used parameters to characterize a resistor. The TCR defines the change in resistance as a function of the ambient temperature. The common way to express the TCR is in ppm/°C, which stands for parts per million per centigrade degree. The temperature ...


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Assuming you fix the temperature at the cell boundary, you can solve for the steady state temperature profile within the cell using (see any elementary heat transfer book) $$\nabla^2 T = -\frac{\dot q}{k}$$ where $k$ is the thermal conductivity on the inside of the cell and $\dot q$ is the heat generation rate per unit volume. The temperature only varies ...


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Moving water doesn't freeze as fast as still water. Boaters who leave their boats docked in bodies of water that freeze over install bubblers at the dock to keep the water moving. The effect is that the immediate area around their boat doesn't freeze over. It's the same principle for running water through you faucet to prevent a freeze. That is part one ...


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Yes, these thermally generated currents (Johnson noise) generate magnetic fields. This means that even non-magnetic materials generate a very-small magnetic noise if they are conductive. This actually places a limit on very-sensitive magnetic field measurements in shielded environments because the shields are usually conductive. The following Review of ...



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