<p align="right">Last Update: <font color="#4f81bd">November, 25, 2024</font></p>
## BIG IDEAS
- A black body is an idealized object which absorbs all [[Wavelength|wavelengths]] of light and emits its own unique wavelength based on temperature.
- The [[Ultraviolet Catastrophe|ultraviolet catastrophe]] is the disconnect between classical theory (intensity changes based on the wavelength) and the experimental results.
### EXAMPLES
Coal
An iron stove
### Classical Explanation
Any object with a temperature above absolute zero emits light at all wavelengths.
- Emission is the passing of heat energy.
- Reflection is the blocking of incoming thermal radiation and returning it back.
Classical physics relies on the formula for intensity ($I$).
$I = \frac{2kT}{(\lambda)^2}$
Where
$k$ is the Boltzmann’s constant,
$T$ is temperature, and
$\lambda$ is wavelength in meters.
- an increase in T will increase Intensity (energy).
- a decrease in $\lambda$ will increase Intensity (energy).
### Predicted vs Actual Results
Classical physics predicts a very small wavelength would lead to greater intensity. However, a plot of intensity versus wavelength shows a peak with a drop in intensity at lower wavelengths.
The shape of the curve cannot be described by classical physics.
![[Actual vs Predicted Graph.png]]
An increase in intensity happens with a temperature increase, and the peak shifts toward the ultraviolet parts of the spectrum.
The shift of the peak to ultraviolet led to the name ultraviolet catastrophe.
### Planck's Equation
[[Max Planck]] solved the problem of the [[Ultraviolet Catastrophe]] by suggesting radiant energy is emitted in [[Quanta|quantum units]].
$E = nhf = \frac{nhc}{\lambda}$
where
- $n$ is a non-negative integer
- $f$ is [[Frequency|frequency]]
- $h$ is [[Planck’s constant]] ($6.63 x 10^-34 J \cdot s$)
- $c$ is the [[Speed of Light|speed of light]] ($3.0 x 10^8 m/s$)
- $\lambda$ is [[Wavelength|wavelength]]
- In [[Classical Physics|classical physics]] [[Energy|energy]] can have any value. In [[Quantum mechanics|quantum physics]], energy has discrete values.
- Quantum energy depends on frequency, not intensity.
### Video
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### Related Topic
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