The temperature-dependant emission of electromagnetic waves. Combine this tag with [tag:thermodynamics] for a macroscopic view or [tag:quantum-mechanics] for a microscopic explanation.

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0answers
32 views

how could the sun photons be the source of light to our vision? [on hold]

if the atom has 99.99% empty space and the photon has no mass while our universe is 2dimensional flat so how could the sun photons be the source of our vision? how could photons be reflected by ...
-1
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2answers
55 views

If heat can't be transformed into other forms of entropy, why do hot things radiate electromagnetic waves?

The laws of entropy says entropy can only increase. On the other hand, if I take a hot object, it will naturally convert its heat into EM radiation. How is this possible? Does EM radiation count as ...
0
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1answer
80 views

How does the hot cup of tea cool down? [duplicate]

I am not sure about my answer. I think that the cup of tea cools down by the following modes: Radiation between the surface of the tea and the air molecules. Conduction between the tea and the cup ...
1
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3answers
43 views

The thermal expansion of material

The question is that: they drill a hole in the middle of a metal. Then when this metal is heated, will the hole become larger or smaller? The hole will get bigger, by experiment, but I think that when ...
3
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0answers
68 views

Would a rocky planet orbiting so close to a very hot star eventually vaporize?

I was thinking about the physics behind a hypothetical scenario where a planet the size and the mass of the Earth is orbiting so close to a very hot star and what the long-term fate of such a planet ...
3
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1answer
22 views

Computing color and brightness of a hot material

Every blackbody color calculator I've managed to find only calculates hue and saturation; they completely ignore brightness, which severely limits their usefulness if you're trying to model the actual ...
26
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3answers
3k views

How many X-rays does a light bulb emit?

I read somewhere that most things1 emits all kinds of radiation, just very few of some kinds. So that made me wondering whether there is a formula to calculate how many X-rays an 100W incandescent ...
0
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1answer
45 views

What is the wavelength of a hot metal when its temperature 400 C? [closed]

I would like to know what will be the wavelength of a hot steel which temperature is 400 degree C
3
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1answer
83 views

An object glows red at around 1000K while a red star is around 3000K. What causes this misalignment in spectra?

According to the H-R diagram, a red star is 3000K, a yellow star is 6000K and a white star 10000K. But a hot metal appears red at 1000K, yellow at 1500K and white at 2000K.(approximately) Why is ...
0
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0answers
29 views

Is there a Lagrangian that can lead to the Rayleigh-Jeans law?

Is there a way to derive the Rayleigh-Jean's law using classical statistical mechanics only? On the internet there is a common way to arrive at the equation by using concepts in electrodynamics. This ...
3
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2answers
64 views

Second Law of Thermodynamics and heating a blackbody with another blackbody

Given a large blackbody with surface area $A_1$ and temperature $T_1$, let's assume I can use some mirror and lens system to capture all the emitted radiation and transfer this energy to a smaller ...
1
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0answers
26 views

When can we assume a body to behave like a black body?

In an experiment I estimated the temperature of a Tungsten bulb filament measuring the resistance of it, and tried to verify whether the power of the filament is proportional to the fourth power of ...
1
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1answer
70 views

Calorimetry - Emitted Joules [closed]

How can one calculate the total amount of emitted joules from an object with a temperature that isn't constant? A great start is this formula: ...
0
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0answers
23 views

Is there an acoustic Black Body Radiation?

Imagine a cavity in a infinitely extended solid filled with another type of solid in thermal equilibrium. Are there statistics for phonons equivalent to the Black Body Radiation by Planck?
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0answers
24 views

Counting modes Rayleigh-Jeans

In the derivation of the Rayleigh-Jeans Law, we count the number of EM modes in a square cavity. After calculating the number of allowed modes due to boundary conditions, we multiply it by a factor of ...
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1answer
57 views

Explain Stefan-Boltzmann Law?

Can someone explain the Stefan-Boltzmann law in an easy-to-understand way?
1
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1answer
126 views

Is Ronald Ace's “solar trap” patent plausible?

This newspaper article and a few others from last year discussed a patent by independent US inventor Ronald Ace. It's about a kind of absorber for solar thermal energy systems, and it's supposed to ...
2
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0answers
31 views

Car Heating due to the sun: comparison of different contributions

Let's imagine that we need to choose a car in order to minimize the Temperature that the inner part of the car will reach after some hours under the sun. We know that two factors (if we suppose that ...
0
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1answer
39 views

Heat transference in my lunch [closed]

Say that I have a hot sandwich and a cool salad, both in functionally-identical plastic containers that provide no effective heat insulation. I need to stack these two containers for ease of ...
4
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0answers
36 views

Temperature modelling

I have to find a mathematical model for the temperature vs. time to study the temperature of the environment next to a lamp. This lamp is made off and on on, let's say, a daily basis The lamp is ...
0
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1answer
70 views

Temperature of planets without atmosphere

I am wondering how come a planet without atmoshhere loses heat in space when the space around it is a vacuum. In my understanding for one object to lose heat it must have contact with another ...
1
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2answers
40 views

Classical absorption of radiation

How does electromagnetic radiation get absorbed by an object (like a black body) in the classical regime? In the classical picture, electromagnetic radiation is produced by the movement of charges, ...
0
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2answers
63 views

Radiation from home heaters [closed]

My understanding of radiation is energy being emitted from a source. So much radiation would come out of a home gas or oil heater to become dangerous. I'm assuming infrared radiation.
2
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1answer
51 views

Is UV catastrophe same as IR catastrophe?

I am currently studying quantum physics from Serwey-jewet. Where in the topic of Planck's law, infrared catastrophe is alternatively used for UV catastrophe while explaining how Plancks constant ...
1
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1answer
33 views

How can I find the radiance over a finite range of wavelengths using Planck's Law?

I'm working on a small programming project involving Planck's Law, and I keep getting errors. I'm fairly certain this is due to a misunderstanding of physics on my behalf. Basically, I am trying to ...
12
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2answers
326 views

Will Neil Armstrong's moon boot marks really last for thousands of years?

This question concerns the residual heat (if any) contained within the Earth's moon. At the time of the Apollo moon landings, it was widely reported that the boot marks left by the astronauts would ...
2
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0answers
23 views

In theory, Is it possible irradiate a blob of matter -for instance- with microwaves in order to that matter emit more energy than has received?

Suppose that you want coerce a block of matter to lose his energy. I mean thermal energy. This should be done by irradiation of more energy. The final thermal energy should be lower that the original ...
2
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3answers
258 views

I don't understand black body radiation graphs

Let's look at the above graph. This black body graph is for the temperature of 5000K. Each temperature has a different black body graph? How am I supposed to read this graph? Do I start from the ...
3
votes
3answers
889 views

How does the heat of Sun come on Earth when there is no medium?

Sun is the most important source for life on Earth which gives sunlight and heat on Earth. But I was wondering like how does the heat of Sun come on Earth when there is no medium out there in space?
2
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1answer
91 views

How fast does heat travel via conduction?

I have read this question which seems to ask an identical question, but I'm not sure - it had far too many words I don't understand, let alone the equations. Perhaps someone can answer with a ...
2
votes
3answers
63 views

Different materials have different temperatures?

Why do two materials, under the same weather, have different temperatures? I have a small clue about it. For example, iron and wood supposed under the sun's radiation, and if we touch both of them, ...
0
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1answer
48 views

Quantization in Black Body Radiation [duplicate]

Why does energy need to be quantized to explain black body radiation? Wouldn't the approximate normal distribution of the kinetic energy of particles at a certain temperature be sufficient, ie. few ...
20
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6answers
540 views

Black Body Golf Balls

The surface of a golf ball has about 35% more surface area (than a similar sphere) due to its dimples. So my question is simple, given identical radius, ideal black body material, and temperature: ...
0
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3answers
149 views

How exactly does wave theory of light fail to explain blackbody radiation? [duplicate]

I don't really understand the reason why wave theory of light fails to explain the blackbody radiation. My textbook says the Planck's quantum theory explains blackbody radiation. It says "If we ...
0
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0answers
34 views

Am I very wrong with my grey body calculations?

I'm trying to calculate the maximum heat that an object on the moon can reach with the energy provided from Sunlight. I've got a total power output of the sun per square meter at the distance of the ...
0
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1answer
89 views

How long does a black hole last after it becomes white hole?

According to Stephen Hawking's theory of black holes, once a sufficient mass has been lost through evaporation, the escape velocity $3 \times 10^8$ meters per second so light is able to escape from ...
2
votes
1answer
221 views

Highest temperature possible to achieve using magnifying glass and sunlight [duplicate]

Temperature of the surface of the sun is about 5750K. Can you heat an object to more than 6000K using magnifying glass and sunlight? According to second law heat cannot be transferred from colder to ...
0
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0answers
13 views

how can I compute the temperature of a metal (iron / steel) rod when a current is applied?

I would like to compute something like $T(j,l,R)$ where $T$ is the temperature of the rod, $j$ the current, $l$ the lenght of the rod and $R$ the radius of the rod. there is any difference if the rod ...
2
votes
2answers
58 views

Do the outer gas planets radiate their mass?

We know that the sun experiences angular momentum loss, and radiates a portion of it's mass (though helicity is conserved). Can we say the same about massive Jupiter, or even Saturn, Uranus or ...
1
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1answer
36 views

Relation between temperature and black body radiation

How can one derive the amount of light as well as the shortest wavelength of the emitted light from the temperature of an object due to black body radiation? Shouldn't the amount of light emitted ...
2
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1answer
86 views

2nd law of thermodynamics - thought experiment

I have designed this simple thought experiment that seems to contradict 2nd law of thermodynamics. Could you please find a mistake in my reasoning? ...
1
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1answer
28 views

Understanding view-/formfactor for radiation with a specific example

There is radiation coming from a point source (black body). How much of the total emitted energy (from the point source) hits a spherical surface given by $\phi = 0 - \pi $ and $\theta = 0 - \pi/2 $? ...
1
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1answer
104 views

Rayleigh-Jeans Law

My question is simple, why do we believe Rayleigh-Jeans law to be absurd? Is the Ultra-violet catastrophe incorrect or is it only because we can not create or know of a perfect emitter? I am a bit ...
4
votes
1answer
127 views

Blackbody cavity relationship between energy of oscillators and EM radiation

This question is based on Planck's view of blackbody radiation in a cavity. Here is a quote from here: ...where $\langle E \rangle$ is the average energy of the oscillators present on the walls of ...
2
votes
1answer
66 views

Planck's postulate for oscillators or for light?

I know that Planck originally postulated that the energy of an oscillator in a black body was quantised to $E=nh\nu$ but did he know at the time that this meant the energy of light was also quantised ...
0
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0answers
25 views

Polarisation states in 1d?

I am working through a derivation of the spectral energy density in a 1d cavity. The derivation says that the number of modes (per unit volume) in a frequency interval $dv$ is given by: $$g(\nu)d\nu ...
1
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1answer
32 views

Measured temperature (thermometre set to emissivity of 1) of smooth surface too high or to low?

We want to measure the temperature of a smooth flat surface with a thermometre based on absorption of thermal rays. The emissivity setting of the thermometre is set to 1 (same as a black surface), ...
2
votes
3answers
83 views

Why stars are white? According to Rayleigh Scattering

According to Rayleigh Scattering, the red waves are capable of travelling a long distance, so that only we are seeing the Sun as reddish during Sunset and Sunrise. If this was true then all other ...
1
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2answers
184 views

How did Planck derive his formula $E=hf$?

Some time ago I asked my quantum physics lecturer the question: How did Planck derive his formula, the Planck–Einstein relation $$E=hf$$ with constant of proportionality $h$, the Planck ...
1
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1answer
75 views

How much work can we extract from a black hole?

Recently, I've read an article on scientific regarding the possibility of a stairwell into a blackhole (unsurprisingly, it isn't possible). I've found the following question more interesting: ...