Blackbody radiation and Planck’s law

Equipment

• Planck spectrum plot versus frequency/wavelength
• Virtual radiation cavity with oscillating modes
• Sliders for temperature, density/frequency, and mode count

Procedure

1. Observe the spectrum vs temperature

   Drag "Temperature" from low to high and follow the spectrum in figure 1 and the cavity modes in figure 2. Read the temperature readout; note the peak shifting toward higher frequencies and the amplitude rising steeply as T grows.

2. Check Wien's displacement law

   Estimate the peak position $\lambda_{max}$ (or $\nu_{max}$) at two temperatures and check $\lambda_{max}T = b \approx 2.898\times10^{-3}$ m·K: doubling T halves the peak wavelength. Record the data pairs from the readout/plot.

3. Check T⁴ and the classical limit

   Compare the area under the spectrum (total brightness) at two temperatures: the ratio should be near $(T_2/T_1)^4$ per Stefan–Boltzmann $P = \sigma T^4$. Vary "Number of states"/"Density" and note the high-frequency tail cuts off as $e^{-h\nu/k_BT}$ — the very "ultraviolet catastrophe" Rayleigh–Jeans could not avoid.

Simulation

Experiment history

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