# Tagged Questions

Heat is energy transferred from one system to another by thermal interaction. In contrast to work, heat is always accompanied by a transfer of entropy. Heat flow is characteristic of macroscopic objects and systems, but its origin and properties can be understood in terms of their microscopic ...

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### Microwave oven heating time

It's logical to think that the time it takes a microwave to heat the food would be proportional to the mass heated. But since a microwave is based on dielectric heating, I think that if you increase ...
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### Dividing values with units

I'm reading about the subject of heat in a basic physics book. If I am not mistaken the formula to work out how much energy is required to increase the temperature of water is ...
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### Question about the proof that heat capacity goes to zero if temperature approaches $0K$

I don't completely understand the proof that is given for the claim that the heat capacity goes to zero, if the temperature approaches $0K$. They do it as follows, if $C_x$ is the heat capacity where ...
456 views

### Finding electric power generated using heat transfer

I'm working through an example I have been given to study. Suppose I have a 2m X 4m photovoltaic panel on my roof that is irradiated with a solar flux of $G_s = 700W/m^2$. Given: $\alpha_s = 0.83$ ...
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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 would a change in ambient temp affect a radiator?

I'm curious if you have a radiator or say a block of metal (lets say it's copper since it has the highest thermal conductivity) and on one side is a processor producing heat. At idle the processor ...
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### Why is it faster (as in proportion to volume) to boil 4 cups of water than to boil 2 cups?

I did an experiment where I boiled two cups (500ml) of water in a kettle, and it took 1:30 minutes to reach around 98 C, average. However, when I boiled 4 cups of water, (1L) it only took me 2:30 ...
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### Electric power transmission

If we want to transmit electic current for a long distance, we must minimize a heat that releases because of the resistanse. We cannot make a cable wide because it is expensive and it will be massive. ...
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### Find the workdone to increase the temperature of an ideal gas by 300c if gas is expanding under [closed]

Find the work done to increase the temperature of an ideal gas by $30^o C$ if gas is expanding under the condition $V \propto \dfrac{t^2}{3}$.
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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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### Heat deposition at optical focus in a clear medium

This is an applied physics question for an engineering problem. The well known experiment we have all done--burn paper and wood with a magnifying glass and the sun's rays. My question is, if one were ...
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### LED Thermal Modeling (How to solve heat equation with constant heat source)

I have a mechanical design with LEDs that generate heat. I want to estimate the temperature at the LED junction vs. time, but especially at steady state. Knowing the LED voltage drop and current, I ...
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### Is it 11% hotter today than it was yesterday?

Yesterday the temperature outside was 0.5 °C. Today, the temperature is 30 °C. 30 is 5300% more than 0.5, but today is obviously not 5300% hotter than yesterday. In Fahrenheit, the temperatures are ...
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### Mechanical Equivalent of Heat

Recently I have been looking up James Joule's experiment regarding the mechanical equivalent of heat. After viewing some drawings of the apparatus, I assumed that the lines holding the weights would ...
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### Total massflow through heat exchanger

I am working on a project and I stumbled on a problem. The project is to design a heat pump to replace the old system (actual problem, not some homework problem). There are 100 or so induction units ...
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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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### Reflectivity of a glowing-hot metal surface

When a polished piece of metal (or steel in particular) is heated to incandescence, how do its reflective properties change? Given a mirror-like surface, would the object temporarily cease to act ...
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### Does more reflective aluminum foil make a room cooler compared to less reflective foil?

Aluminum foil is said to be not absorbing light at all. It reflects light. So, does it mean that a more shiny aluminum foil will reflect more light and thus make the room more cooler as compared to ...
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### Is the heat required to alter the Higgs field an 'absolute heat'?

I have read and heard that manipulating the Higgs field would require heating up a local geometry to ridiculous temperature. I am trying to understand if there are stars or places in the universe ...
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### Heat transfer in fluid between two horizontal plates vs unconfined case

I often see the correlation for turbulent heat transfer between liquid cells published by Globe and Dropkin (1959). In the original paper the fluid was confined between two horizontal plates and ...
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### Beginner Thermal Dynamics Question [closed]

A syringe is set up filled with air (mainly N2 and O2) as shown in the diagram below. The surface area of the syringe is 15.3 cm2. The initial pressure inside the syringe is Pi = 114 kPa and the ...
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### How can I understand a Vortex Tube and its efficiency?

A Vortex Tube takes a pressurized input stream, most typically of a gas, and creates two output streams with a temperature differential. Apparently, it has been described as a Maxwell's Demon. Both ...
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### Calculate how hot PLA will become

I am trying to attach the shaft of a brass heating tip to a PLA component. My problem is that the tip will have to reach a temperature of about 200°C and the PLA can only handle a temperature of about ...
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### Cooling a cup of coffee with help of a spoon

During the breakfast with my colleagues, a question popped into my head: What is the fastest method to cool a cup of coffee, if your only available instrument is a spoon? A qualitative answer would ...
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### Optical element is heated by laser: is it possible to get oscillating heat distribution?

Imagine that we have thin optical element, which is irradiated by laser. Laser heats element, so there is some heat distribution in element. There is a heat sink through upper and lower element faces ...
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### Indicators on how even the heat is distributed?

I'm wondering if there are any good indicators on how even the heat is distributed on an object (for simplicity, a flat object maybe)? What are the possibly reasonable ways to maximize the evenness if ...
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### How do whisky stones keep your drink cold?

From a discussion in the DMZ (security stack exchange's chat room - a place where food and drink are important topics) we began to question the difference between how ice and whisky stones work to ...
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### Calculating the change in entropy in a melting process

I have a homework question that I'm completely stumped on and need help solving it. I have a $50\, \mathrm{g}$ ice cube at $-15\, \mathrm{C}$ that is in a container of $200\, \mathrm{g}$ of water at ...
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### Could we really charge metal plates using microwaves?

While skimming through Dielectric heating, I read that they use microwaves to charge the plates. How do they do that?
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### Calculating the coefficient of thermal expansion in liquid

I am trying to write a matlab function that calculates the coefficient of thermal expansion of water from a given temperature. From what I understand the thermal expansion coefficient is calculated as ...
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### Why is an air conditioner more efficient in a low-thermal-mass house?

Why is an air conditioner more efficient in a low-thermal-mass house? I recently read To get these efficiency gains it is important to use the air conditioner as it is intended: the unit has to ...
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### How do I calculate the heat lost or gained by surroundings? [closed]

How do I calculate the heat lost or gained by surroundings (Q surr) given mass ($m$), change in temp ($\Delta T$), and specific heat ($c$)? What equation would I use? How can I tell whether it's lost ...
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### Does darker skin color make it easier to live under sun? [migrated]

I have always thought darker colors absorb more heat from the sun, so if you are wearing a white T-shirt you will be cooler under sun than wearing a darker T-shirt, or a black piece of steel will be ...
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### How can anything be hotter than the Sun?

I've heard that if a space shuttle enters the atmosphere from a bad angle its surface will become so hot that it will be hotter than the surface of the Sun. How can that be? It seems to an uneducated ...
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### The effects of heat on gravitational fields

In boiling soapy water, globs of soap coalesce as the temperature increases to boiling. Does this mean that temperature increases the gravitational pull of bodies?
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I am studying heat transfer And understanding the vacuum flask example that involves conduction, convection, and radiation Do you know other example that involves these 3 phases? we can name some by ...
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### Why not assimilate nuclear waste into “igneous” rock?

I was reading a question about why not to drop nuclear waste into volcanoes; the short answer is it would come back out and not be rendered safe. Ignoring the cost and energy requirements, why can't ...
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### Time constant of ice melt

I'm familiar with problems of "how much ice can you melt given some amount of energy", but I'm writing to get some clarification on the time constant of this event. This question might be somewhat ...
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### Newton's cooling law

I want to know few things regarding the practical of Newton's cooling law. 1). What are the other possible ways of making external conditions constant except using two calorimeters one within one? ...
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### Does electrically heated water have an adverse effect on hair?

I know I should have asked this question on a different site. but this was the most suitable site available right now for my question. Perhaps after this proposed site goes on Beta, we can move it ...
3k views

### Is fire plasma?

Is Fire a Plasma? If not, what is it then? If yes why, don't we teach kids this basic example? UPDATE: I probably meant a regular commonplace fire of the usual temperature. That should simplify ...
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### Calculate the amount of water needed to extinguish a vehicle fire? [closed]

Essential Data: Petrol has a calorific value 45000 KJ/Kg Temperature at which petrol burns ~ 300 Degrees Celcius Specific heat Capacity of Water = 4.2 KJ/Kg Specific heat Capacity of Steam = 2.0 ...
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### What happens to pipe outlet temperature here?

I have a fluid flowing through a pipe in the ocean and there is heat transfer from the ocean to the fluid in the pipe. I prepared a simulation and the results show that if I increase the mass flow ...
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### What would result in a transformer that has its secondary wires disconnected from any circuit?

I am studying magnetism and I am curious as to what happens in a transformer that has its secondary output wires connected through a circuit versus one that doesn't. My main questions (in the case of ...
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### Heating and Recooling of an Object

Consider a piece of metal of length $L$ and linear thermal expansion coefficient $\alpha$. We eat the metal $\Delta T$ degrees, causing the metal to increase to length $$L' = L + L \alpha \Delta T$$ ...
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### Why does hot oil explode when pouring water on it?

I am puzzled to know, What is the reason of hot oil make sound and explode when we pouring water on it?
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### Heat of adsorption from fugacity data

I have a set of data relating the fugacity ($\approx$ pressure) to the loading for a given set of temperatures. There are three temperature sets each having five fugacity vs. loading points. The ...
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### gravity affecting a molecules speed? [closed]

Why are the poles colder than the rest ofthe planet?Is the gravity stronger making molecules spin slower?How does gravity affect heat and hydrogen bonds? And what affects gravity?A little off topic ...