## Black body [ENDORSED]

(Wien's law: $T\lambda _{max}=\frac{1}{5}C_{2}$ )

My Nguyen 1L
Posts: 11
Joined: Fri Sep 25, 2015 3:00 am

### Black body

Can somebody enlighten me about the concept of black body radiation and how it is related to the planck's hypothesis?! Thank you so much in advance!
P/s: I try to read the book but not quite get the idea of the theories

Ian Hurst 3L
Posts: 22
Joined: Fri Sep 25, 2015 3:00 am

### Re: Black body  [ENDORSED]

To understand planck's constant (and his hypothesis), the formula it is used with (E=hv), and its importance, you must first understand that light rays push and pull on an electron. This creates the "wave" picture that is shown by figure 1.7 in the book. How fast the cycles (created by the push and pull of the electric field in a light ray) occur can be called the frequency (v= 1/s) of the electron.

Next, scientists noticed that as an object got hotter it started to give off different colors of light (the colors of light had different wavelengths). The book states the hot object can be called the "black body". Figure 1.12 in the book shows the energy given off by black body radiation. Notice that the wavelength given in micrometers (10^-6) and the energy density (J x m^-4) will cancel to give intensity (the square of the amplitude, which is given in meters (m)). And in the diagram, as maximum intensity is reached with increasing temperature, the wavelength decreases. This also means that the frequency will be increasing (wavelength x frequency = speed of light).

Another important concept to understand is that electrons can ONLY exist at certain energy levels. And when electrons transitioned between energy levels they would give off energy (electromagnetic radiation).

Planck explained that this energy was given off in packets (quanta). He thought he could relate the high frequency (low wavelength) oscillation (push and pull of electrons by an electric field) of electrons in black bodies to the energy given off. This is shown in his formula (E= hv), which shows that the energy and frequency can be related through "Planck's constant (h)". This constant is 6.626 x 10^-34 J x s.

Hope this helps!

KelseyKobayashi_2M
Posts: 21
Joined: Sat Jul 09, 2016 3:00 am

### Re: Black body

What is the significance of black bodies and will we have to understand all about how they work for the midterm/final?

Rachel Wile 2D
Posts: 49
Joined: Sat Jul 09, 2016 3:00 am

### Re: Black body

A black body is something that absorbs all of the electromagnetic radiation incident upon it. It is an idealized emitter and absorber of energy. It is good concept to know because it may help you understand how other objects absorb/emit electromagnetic radiation better.