Home Optics Experiments PE-1800 Planck's Law

Keywords:

  • Blackbody Radiation
  • Rayleigh-Jeans
  • UV catastrophe
  • Max Planck
  • Wien's approximation
  • Temperature of the sun

 

Basic experiment

Intended institutions and users:

Physics Laboratory

Engineering department

Electronic department

Biophotonics department

Physics education in Medicine

 

Introduction

How it works ...

Downloads

PE-1800 Planck's Law

Educational PE-1800 Planck's Law Kit

It is a well known fact that hot bodies emitting optical radiation from ultraviolet to infrared. The spectrum shows a peak, which depends on the temperature of the body. This phenomenon attracted the scientist Rayleigh and Jeans to find an theoretical model for this. However, all their attempts failed and the correctly formulated solution predicted infinite power in the UV range of the spectral emission. It was Max Planck finding a way out or the so called UV catastrophe by defining a new constant h and accidentally initiated a new physics, the quantum mechanics.

In our experiment we will track some steps which lead at the beginning of the 20th century to a new understanding of the interaction with light and matter. We will use a kind of black body radiator in form of a incandescent tungsten lamp. The emitted light is captured by a spectrum analyser in real time. With a precise current and voltage applied to the tungsten filament the temperature of it is determined. For a series of temperature values the emitted spectrum is recorded and stored for further analysis. The results are compared with Planck's law as well as the Wien's approximation. Since the spectrometer is fibre coupled and very compact the spectrum of the sun can be recorded and based on the results of the previous measurements with the tungsten lamp the temperature of the sun is determined.

 

PE-1800 Planck's Law

PE-1800 Planck's Law How it works

A micro lamp with a tungsten filament is placed into a fibre adapter to which the fibre of the spectrometer is attached. A controller allows the precise setting of the filament current and the measurement of the voltage. To calculate the temperature of the filament the standard equation RT-R0= R0‧ α‧(T-T0) is used. This requires the knowledge about the value of R0 at the temperature T0. For this purpose a temperature sensor measures the temperature T0 of the switched off and cooled down lamp while the resistor R0 is measured and displayed by the controller. After getting this data the spectrometer is connected tor the lamp and a series of spectra is recorded. It should be mentioned that the spectrometer provides raw data without correction of the spectral sensitivity of it. For each recorded spectrum the temperature of the filament is known and the Plank’s law can be calculated accordingly as reference.

PE-1800 Planck's Law

Flag of Germany