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PHYWE Stefan-Boltzmann's Law of Radiation |
Learn about:
- Black body radiation
- Thermoelectric e. m. f.
- Temperature dependence of resistances
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.
The experiment is started by measuring the filament's resistance at room temperature. A resistor of 100O is connected in series with the lamp to allow a fine adjustment of the current. For 100 mADC and 200 mADC the voltage drops across the filament are read and the resistance at room temperature is calculated. The current intensities are sufficiently small to neglect heating effects.
Then, the 100O resistor is removed from the circuit. The filament is now supplied by a variable AC-voltage source via an ammeter allowing measurement of alternating currents of up to 6 amperes. The voltmeter is branched across the filament and the alternating voltage is increased in steps of 1 volt up to a maximum of 8 V AC. Initially, a voltage of 1 V AC is applied to the lamp and the Moll-thermopile, which is at a distance of 30 cm from the filament, is turned to the right and to the left until the thermoelectric e.m.f. shows a maximum. The axis of the cylindrical filament should be perpendicular to the optical bench axis. Since the thermoelectric e.m.f. is in the order of magnitude of a few millivolts, an amplifier has to be used for accurate readings. The factor of amplification will be 102 or 103 when using the voltmeter connected to the amplifier in the 10 V range. Before a reading of the thermoelectric e.m.f. is taken, a proper zero-adjustment has to be assured. This is done by taking the lamp together with its slide-mount away from the bench for a few minutes. The amplifier is used in the LOW DRIFT-mode (104O) with a time constant of 1 s.
After the lamp has been put back onto the bench, the reading can be taken if the Moll-thermopile has reached its equilibrium. This takes about one minute. Care must be taken that no background radiation disturbs the measurement.
With this experiment you can measure the resistance of the filament of the incandescent lamp at room temperature and ascertain the filament’s resistance at zero degrees centrigrade. The energy flux density of the lamp at different heating voltages can be measured and the corresponding heating currents read off for each heating voltage and the corresponding filament resistance can be calculated.
Included with WLS1807-84:
Thermopile, molltype; shielding tube; universal measuring amplifier; variable power supply 15 VAC/12 VDC/5 A; lamp holder; filament lamp 6V/5A; connection box; resistor in plug-in box 100O; optical profile bench; base for optical bench; slide mount; digital multimeter; connecting cords; and manual on CD-ROM.
Included with WLS1807-85:
Thermopile, molltype; shielding tube; variable power supply 15 VAC/12 VDC/5 A; lamp holder; filament lamp 6V/5 A; connection box; resistor in plug-in box 100 O; digital multimeter; connecting cords; barrel base; meter scale; Cobra3 Basic Unit; power supply, 12 V; RS232 data cable; Cobra3; universal writer; and manual on CD-ROM.
System requirements for WLS1807-85:
PC, Windows 95 or higher
For your convenience this experiment is available to you as a complete set.
Everything you require to perform the activities are included in the total price.
For assistance in using your new equipment we also offer professional development (WLS1808-24) on all PHYWE line products.
For customization options and pricing please contact your local Cenco representative.
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