# Tagged Questions

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### A Calorimetry Problem

I have a question in calorimetry from an old competitive exam. The question is: The temperature of $100$ grams of water is to be raised from $24 ^\circ$C to $90 ^\circ$C by adding steam to it. ...
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### How do you determine the heat transfer from a P-V diagram?

I doubt this question has been addressed properly before, but if there are similar answers, do direct them to me. I am currently studying the First Law of Thermodynamics, which includes the p-V ...
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### Is it possible to condense heat?

Suppose that I have a warm room. Is it possible to condense the heat of the room into a small object so that the room turns cold and the small object very hot? If it's possible: How? If it's not: ...
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### Do photons lose energy while travelling through space? Or why are planets closer to the sun warmer?

My train of thought was the following: The Earth orbiting the Sun is at times 5 million kilometers closer to it than others, but this is almost irrelevant to the seasons. Instead, the temperature ...
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### Is $E=mc^2$ reserved to nuclear physics?

I was wondering, while putting a log in my fireplace, how much energy the piece of wood would give. The most famous formula poped into my head: $E=m \cdot c ^ 2$! Is this formula applicable to a ...
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### What is the difference of work $W$ and thermal energy $Q$ in thermodynamic Stirling-process for ideal gas?

What is the difference of work $W$ and thermal energy $Q$ in thermodynamic Stirling-process (in simple form) for ideal gas? I think that you need work to preserve this process and you bring thermal ...
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### Does closing curtains 'make your home warmer'?

I mean, in the sense that the act of closing curtains would somehow reduce the amount of heat loss of the house to the outside, thus making it warmer for a given supply of heating.
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### Can I take heat from the air and convert it to electricity?

Its a summer day and the air in my house has been heated up. I could switch on my air conditioning, but then I'd be using energy from the grid in order to reduce the amount of energy in my house. ...
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### What arrangement of sound waves would be needed to heat air in a typical sized room?

From what I understand, sound is simply the jostling of the molecules that make up the air in a specific pattern, widely known as waves. I also know that these are longitudinal waves. If we were to ...
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### What would jumping into a pool and feeling cold be called? Conduction, or convection?

This was another question from my son's workbook. It said: ...
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### Why can't I evaporate water without wind, just heat? (not boiling,evaporating!) Or can I?

So here is the thing, I searched all over the internet for this but all the sources say that I need wind because the process of evaporation goes as follow: Water particles at the top layer with ...
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### What is the difference between infrared heat and “regular” heat?

In Feynman's terms temperature is the speed at which atoms are 'jiggling'. Now, let's suppose I've just eaten a sizable dinner, and my body temperature just got a tad up. Am I emitting more photons in ...
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### Where does the lost energy go in a rubber band powering a rotating shaft?

Okay, I'm no physics whiz, and this has me stumped. You know those toy airplanes you can get with the rubber-band driven propellers? You twist the propeller a bunch of times, and this stores ...
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### Heat Equation Equalities

While studying the heat equation, I ran into a few equalities that I cannot understand. For example, Fourier's law of heat conduction claims that $$\varphi(x,t)=-K_0\frac{\partial u}{\partial x},$$ ...
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### How can there be heat in a vacuum?

I keep reading in the Physics World focus issue on vacuum technology about scientists creating high temperatures in the vacuums etc. If heat is caused by thermal energy being radiated from particles ...
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### how does heat energy start to speed up a gas molecule?

If it was possible to place a single gas molecule in a cell and freeze it to near absolute zero. What would the molecule do as it thawed out? Would it translate the heat energy into it's electrons ...
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### 2d or 1d conduction in this scenario?

There is a rectangular fin attached to a heat exchanger with a base temperature of 350K. The fin has uniform properties and experiencesa uniform heat generation. It also experiences heat transfer with ...
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### At what point can we assume the tip of a fin is adiabatic?

Let's say there is a fin that is 1mm thick, extends 8mm from the surface, and is 10 mm wide. The fin is exposed to a moving fluid. Can we assume the adiabatic tip condition and use the characteristic, ...
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### In what situations do I use the characteristic length of a fin to find the surface area?

So I'm learning about fins in heat transfer and it seems that there are two separate formulas for the surface area of a rectangular fin of length L, width w and thickness t. The fin is attached to a ...
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### Which is more efficient, heating water in microwave or electric stove?

So our propane tank in the kitchen ran out again today. Which is more energy efficient, boiling water in a microwave on an electric stove? All things being equal i.e. starting temperature and mass ...
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### Is the $mL_c$ value for triangular and rectangular fins the same value?

I am looking at the solutions that my professor put up and I feel that he did something wrong. Here is the question and I will give my stab at the solution so you can see why I think that it is wrong. ...
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### How do I find average temperature given a temperature distribution?

I was told to find the temperature distribution of a wire with a current going through it. So I found $$T(x)=T_{\infty}-\frac{\dot{q}}{km^{2}}[\frac{cosh(mx)}{cosh(mL)}-1]$$ I need to find the ...
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I'm looking for the appropriate term to use for what gets "used up" as potential energy is converted to heat and work. For example, some of the the energy in solar radiation is converted by ...
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### When to use Heat Diffusivity eqn and when to use Fourier's law to find temperature distribution?

Let's say that there is a circular conical section that has diameter $D=.25x$ without any heat generation and I need to find the temperature distribution. Originially I thought I could use the heat ...
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### Temperature change effected by electric heater [closed]

A 40-gallon electric water heater has a 10kW heating element. What will the water temperature be after 15 min of heating if the start temp is 50F degrees. There must be an equation. I can't find it ...
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### why egg cooks slowly in mountains?

A quick Google tells me "Because water boils at a lower temperature at high altitudes". But I am not being able to understand this answer and fill-in the gap. Like, how does an egg cook in the first ...
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### How do we perceive hotness or coldness of an object?

Some objects, especially metallic ones, feel cold on touching and others like wood, etc. feel warm on touching. Both are exposed to same environment and are in their stable state, so some kind of ...
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### How does liquid convert to gas on getting thermal heat energy?

Say for example, when we heat, water converts to steam gas. How does it happen? What happens underneath giving rise to breaking of bond between molecules in liquid state and spreading them in gas ...
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### What happens to the absorbed light energy?

When light comes across with a solid material, some of it is reflected, some of it passes through and some of it is absorbed. I understand the reflection and passing through, but I don't understand ...
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### Can temperature be defined as propensity to transmit thermal energy?

I was recently surprised to learn that defining temperature isn't easy. For a long time, it was defined operationally: how much does a thermometer expand. Also surprising, temperature isn't a ...
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### In summer are the upper storey flats more hot or the lower storey flats?

I have often heard neighbours talking things like in a multi storied apartment, the upper flats are more hot in summer then lower flats (or vice versa?) and similarly for some comparison in winter? ...
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### Limit on geothermal energy that could be extracted before the earth's magnetic field collapsed?

This is more of a theoretical thought-experiment question. Basically, how much geothermal energy can we extract before the loss of the magnetic field makes it a terribly bad idea? Will the ...
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### Can heat be transfered via magnetic field in a vacuum?

Say you want to store hot coffee in a container surrounded by a vacuum. To remove all sources of conductive energy loss the container is suspended in the vacuum by a magnetic field and does not have a ...
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### What energy is transformed to heat when a candle is burned?

What energy is being transformed to heat when you burn a candle?
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### Does opening or closing the window in a non-AC car in the summer affect how much heat is felt inside?

This will perhaps look like a very basic and trivial question. But I find it confusing. As an experience, when you are travelling in non-AC car in summer, have people felt if putting on or putting off ...