Stefan-Boltzmann's law of radiation with an amplifier

Principle

According of Stefan-Boltzmann's law, the energy emitted by a black body per unit area and unit time is proportional to the power "four" of the absolute temperature of the body. Stefan-Boltzmann's law is also valid for a so-called "grey" body whose surface shows a wavelength independent absorption-coefficient of less than one. In the experiment, the "grey" body is represented by the filament of an incandescent lamp whose energy emission is investigated as a function of the temperature.

Benefits

• Classical experiment for studying black-body radiation
• High-precision measurement due to special, Moll-type thermopile

Tasks

1. To measure the resistance of the filament of the incandescent lamp at room temperature and to ascertain the filament's resistance R0 at zero degrees centrigrade.
2. To measure the energy flux density of the lamp at different heating voltages. The corresponding heating currents read off for each heating voltage and the corresponding filament resistance calculated. Anticipating a temperature-dependency of the second order of the filament-resistance, the temperature can be calculated from the measured resistances.

Learning objectives

• Black body radiation
• Thermoelectric e. m. f.
• Temperature dependence of resistances