1. Phy100: Blackbody radiation
Goals:
To understand radiation spectrum (power versus wavelength);
To understand the radiation power (power versus temperature).

2. Radiation
Heat can also be transferred by radiating light (i.e. photons) or electromagnetic waves with different wavelengths.
For an object with temperature T or a blackbody,
Q1: What kind electromagnetic waves are emitted (visible or invisible) ?
Q2: How much energy emitted per second per unit area, i.e. radiation power?

3. Basics of waves The distance between two adjacent crests = Wavelength.
The number of crests one observes at a given point per second =Frequency
Wavelength X Frequency = Speed of waves

4. About radiation:
Radiation as a self-propagating electric and magnetic (EM) wave.
2) EM waves travel at the speed of light c=3 X 10^8 m/s or 300,000km/s (Boeing Jet cruise speed about 0.3km/s)
Both electric fields and magnetic fields oscillate as a function of time and spatial coordinates. These waves consist crests and troughs.

5. Full range of forms of radiation

6. Q1
Radio frequency electric signals are electromagnetic waves within the frequency range of 3Hz and 3 GHz. The corresponding range of wavelengths (=c/ f ) are
10cm to 10^8 m;
1mm to 1m;
10^{-6}m to 1mm;
10^{-8}m to 10^{-7}m.

8. Total area below a curve= Total power per unit area
Power density: Power per unit area per unit wavelength
Total area below a curve= Total power per unit area

9. Conclusions Radiation power concentrated in an interval of
wavelength. The peak position in the power spectrum
moves to longer wavelengths when T decreases;
The integrated or total radiation power (the area below the power spectrum) decreases as T decreases.
Wien’s displacement law
Stefan-Boltzmann Law

10. Blackbody radiation at T=310K
Estimate the radiation power of a human body