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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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
47 views

Explain Stefan-Boltzmann Law?

Can someone explain the Stefan-Boltzmann law in an easy-to-understand way?
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1answer
61 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 ...
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24 views

Blackbody thermal radiation [closed]

By definition, the absorptivity of every blackbody radiator equals 1.0 (100% of the incident radiation is absorbed). So from this fact, you can conclude that the reflectivity and transmissivity of a ...
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26 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 ...
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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 ...
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0answers
34 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 ...
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1answer
64 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 ...
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2answers
38 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, ...
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2answers
61 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.
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1answer
47 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 ...
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1answer
26 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 ...
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2answers
315 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 ...
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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 ...
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3answers
227 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 ...
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3answers
829 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?
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1answer
82 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 ...
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3answers
61 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, ...
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1answer
46 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 ...
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6answers
522 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: ...
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3answers
133 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 ...
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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 ...
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1answer
78 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
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1answer
182 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 ...
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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 ...
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2answers
57 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 ...
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1answer
28 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 ...
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1answer
85 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? ...
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1answer
26 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 $? ...
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1answer
95 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 ...
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1answer
123 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 ...
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1answer
60 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 ...
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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 ...
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1answer
26 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), ...
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3answers
79 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 ...
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2answers
172 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 ...
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1answer
67 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: ...
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1answer
102 views

How does an infrared thermometer actually calculate temperature?

I am slightly confused about infrared radiation and the equations related to it. $P = A \epsilon \sigma T^4$ (1) and $B_{\lambda}(\lambda,T) = \frac{2hc^2}{\lambda^5} \frac{1}{e^{\frac{hc}{\lambda ...
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1answer
27 views

How to combine contributions of individual type of cone cell sensitivity to get the human luminosity function?

As shown in this figure from some computer vision book: The data of three types of cone spectral responses is pulled down from: http://cvrl.ioo.ucl.ac.uk/cones.htm It is said that the Long, Medium ...
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1answer
43 views

Ideally black plates

Let's consider $m$ ideally black, thin, infinite plates. Let $T_i$ be the temperature of the $i$-th plate. For given $T_1 > T_m$, why is the radiant flux between any two adjacent plates the same ...
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1answer
60 views

What are the units of color matching functions?

In some computer vision book I read lately, the color matching function is invoked without clear definition of its units. I suspect the color matching functions are spectral irradiance or spectral ...
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2answers
144 views

Blackbody radiation and emissive power

According to blackbody radiation theory, and thanks to Planck, we now know that there is a energy density, $u(\lambda,T)$ [$J/m^3$], associated with a certain wavelength at a particular temperature. ...
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2answers
1k views

Why is pale coloured skin said to absorb more UV?

Many resources state that light skin/pale skin absorbs more UV than dark-colour skin. Doesn't black absorb maximum radiation? For an example, see this article: Natural selection therefore ...
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2answers
52 views

Is shape of a black body much of a concern in physics?

When I read a book on computer vision, I stumble upon the ideal black body model. Using Lambert's cosine law (wiki), one is able to compute the intensity of an area element dA w.r.t. some observer. ...
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5answers
992 views

What exactly is fire? [duplicate]

What is fire? Is it a wave or is it matter? Where does fire come from? Does everything burn with fire? (for example: water and some metals don't burn).
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1answer
250 views

Relationship between temperature and wavelength?

I am investigating the relationship between wavelength and temperature. As seen the figure below of Planks law What is the relationship between the lambda(max) and Temperature? or in simpler ...
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2answers
1k views

What happens to a body, initially at 300K, kept in isolated space? Will it's temperature drop to 0k?

With regards to Thermal Radiation, given a stable body initially at 300 Kelvin placed in isolation, after continuous Thermal Radiation will it's temperature gradually reduce to 0 kelvin ...
6
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2answers
1k views

What would it be like “inside” a star?

This question was triggered by a discussion regarding the computer game Elite: Dangerous, where spaceships routinely operate in close proximity to stars (two or three light seconds away), at which ...
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1answer
35 views

Minimum wavelength in black body radiation

Is there a minimum wavelength in a black body's radiation? If yes, is there a formula to calculate it? In this image from Wikipedia, it does seem that the curve is touching the x-axis rather than ...
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4answers
526 views

I don't understand why a cavity with a hole is a black body [duplicate]

It makes no sense to me that a cavity with a hole is identical to a black body. Sure, the cavity will probably be a near perfect absorber, but I don’t see how it will be a perfect emitter as well. ...