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4

The question doesn't say exactly what is meant by darkest, but it seems reasonable to interpret the brightness as the intensity of radiation from the object. In that case the relevant equation is the Stefan-Boltzmann law: $$ J = \varepsilon\sigma T^4 $$ where $\sigma$ is the Stefan-Boltzmann constant and $\varepsilon$ is the emissivity. The emissivity of a ...


3

Toasting not only browns the surface, it dries out and cooks the interior. Any method that applies heat to the surface and waits for it to diffuse into the interior is limited by the rate of diffusion. You can speed it up by a higher surface temperature, but this leads to uneven cooking. Radiation and particles can penetrate to the interior, and can be ...


0

Turbine is a device with steady flow process and it has one inlet and one exit. First law of thermodynamics for a steady flow process with one inlet and one exit is as below $$q-w=(h_e-h_i)+\frac 12\left(V_e^2-V_i^2\right)+g(z_e-z_i)\;\tag 1$$ Potential energy change is negligible for this device. Usually, kinetic energy change isn't negligible but it seems ...


0

First a couple of pointers to show that the final result on the HyperPhysics website is not unreasonable. In the derivation given in the HyperPhysics website the number of modes is found to be $N = \dfrac{8 \pi L^3}{3 \lambda^3}$ and because $\nu \lambda = c$ where $\nu$ is the frequency and $c$ is the speed of light the equation for the number of modes ...


0

Temperature is a measure of how much energy photons have $E = h\nu$ $= kT$, and the temperature reflects the energy of the photon incident on the detector. The total irradiance or EM power incident on an area $A$ is $P = \epsilon\sigma AT^4$ from Rayleigh-Jeans law. Here $\sigma$ is the Stefan-Boltzmann constant and $\epsilon$ the emissivity of the body. ...


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there are lots of good books in thermal radiation, read Modest for example Author : M Modest Release Date: 15 Mar 2013Imprint:Academic PressPrint Book ISBN :9780123869449 eBook ISBN :9780123869906 Pages: 904Dimensions: 276 X 216



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