Home Optics Experiments PE-1700 Planck's Constant

Keywords:

  • Black Body Radiation
  • Photoelectric Effect
  • Max Planck
  • Visible Diode Laser
  • Phototube • Electrometer

 

Basic experiment

Intended institutions and users:

Physics Laboratory

Engineering department

Electronic department

Biophotonics department

Physics education in Medicine

 

Introduction

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PE-1700 Planck's Constant

When Max Planck "introduced" a useful constant to solve the problem of the UV catastrophe he was not aware that he paved the way to quantum mechanics. After the experimental verification the small letter h became famous and denoted a new natural constant. According to his own words Planck used it as a formal requirement to solve the problem and proposed the famous relation E = h·ν. The value of h has been measured by many scientist to that times and still students learn to understand this constant by relatively simple experiments. One possibility is to find the energy of light with a known frequency. The related energy will be determined by using the photo electric effect with a suitable photo cell. Classical students experiments are using a white light source and a set of narrow band interference filter to obtain a defined wavelength. However, such a white light lamp and the required filter are very costly when compared to modern diode laser. Our experiment is equipped with a set of visible laser diodes of 405 nm, 445 nm, 520 nm, 635 nm  660 nm and 785 nm. The emission of each diode is not collimated and the output power below 5 milliwatt so that laser safety aspects can be neglected. A control source for the diode laser as well as for the photocell is provided along with high precision voltage and current analogue digital converter to measure the energy of the photons with different known wavelength. The slope of the linear fit of the measurement result yields the constant h.

PE-1700 Planck's Constant

 

 

PE-1700 Planck's Constant

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