There are three bodies $a,b,c$ which are discs of diameter $2m,4m,$ and $6m$ respectively.

Their emitted wavelengths are $300nm,400nm$ and $500nm$ respectively.

Which emission power is maximum ?


closed as off-topic by garyp, Rob Jeffries, Kyle Kanos, sammy gerbil, akhmeteli Jan 29 '17 at 15:26

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    $\begingroup$ Welcome Abinash to Physics SE! Please note that this is not a homework help site, see "homework" questions. It is in any case recommended that you show the efforts you have done for solving your problem. $\endgroup$ – user130529 Jan 28 '17 at 15:53
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    $\begingroup$ Question makes no sense. I would guess you mean that these objects emit as black bodies (or grey bodies with similar emissivity) and that the wavelengths you give are the wavelengths at which the specific intensity peaks (which tells you the temperature from Wien's law)). Stefan's Law then tells you that the emission will be $\propto A T^4$. Can't you figure it out from there? $\endgroup$ – Rob Jeffries Jan 28 '17 at 17:43

A good place to start when you have this type of question is Hyperphysics which is great to get quick answers to general physics questions.

Concerning your question in particular, the radiated power per unit wavelength is

$$\left(\frac {du}{d\lambda}\right)\left(\frac c4\right) = \left(\frac{2\pi \kappa T c }{\lambda ^4} \right)$$

Also look at the Rayleigh-Jeans formula:

$$\left(\frac{2\pi \kappa T v^2 }{c^2}\right)$$ which gives you the radiated power per unit frequency.

Or visit this page: Radiated Energy as a Function of Wavelength .

You could also make sure you grasp the concepts of heat radiation, radiation of energy density and revisit the Stefan-Boltzman law.

In any case there is a load of information about the subject all over the internet, Google can be a great ally.

Hope this helps.

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    $\begingroup$ The OP has not mentioned temperatures or black bodies, so you are just guessing. $\endgroup$ – Rob Jeffries Jan 28 '17 at 17:40

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