Objective: Verify the inverse square law for the intensity of radiation from a source of light
According to the inverse square law, the intensity of radiation from a light source, i.e. the power per unit area, is inversely proportional to the square of the distance from the source. This will be investigated in an experiment using an incandescent light bulb. When the distance from the lamp is much greater than the size of the filament, such a bulb can be regarded as a point source of light. In order to measure the relative intensity of the radiation, a Moll thermopile is used.
![Experiment: Inverse Square Law, 8000691 [UE4050100-230], Intensity of Radiation](/imagelibrary/UE4050100-230/UE4050100-230_01_Experiment-Inverse-Square-Law.jpg)
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for the experimental setup of tubes of series S, 1014525 [U185002], Accessories – Type S](/thumblibrary/U185002/U185002_01_140_140_Tube-Holder-S-for-the-experimental-setup-of-tubes-of-series-S.jpg)
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![Digital Multimeter P1035, 1002781 [U11806], Hand-held Digital Measuring Instruments](/thumblibrary/U11806/U11806_01_140_140_Digital-Multimeter-P1035.jpg)
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![Thermopile, Moll Type, 1000824 [U8441301], Heat Flow and Radiation of Heat](/thumblibrary/U8441301/U8441301_01_140_140_Thermopile-Moll-Type.jpg)
![Stefan Boltzmann lamp, 1008523 [U8490050], Light Sources on Stem](/thumblibrary/U8490050/U8490050_01_140_140_Stefan-Boltzmann-lamp.jpg)
![HF Patch Cord, BNC/4 mm Plug, 1002748 [U11257], Experiment Leads and Cables](/thumblibrary/U11257/U11257_01_140_140_HF-Patch-Cord-BNC4-mm-Plug.jpg)
![Barrel Foot, 1 kg, 1002834 [U13265], Bases](/thumblibrary/U13265/U13265_01_140_140_Barrel-Foot-1-kg.jpg)
![High Voltage Power Supply 5 kV, 1003310 [U33010-230], Power Supplies](/thumblibrary/U33010-230/U33010-230_01_140_140_High-Voltage-Power-Supply-5-kV.jpg)
![Graduated Ruler, 1 m, 1000742 [U8401550], Measurement of Length](/thumblibrary/U8401550/U8401550_01_140_140_Graduated-Ruler-1-m.jpg)
![Measurement Amplifier U (230 V, 50/60 Hz), 1020742 [U8557560-230], Measuring Amplifier](/thumblibrary/U8557560-230/U8557560-230_01_140_140_Measurement-Amplifier-U-230-V-5060-Hz.jpg)
![Barrel Foot, 500 g, 1001046 [U8611210], Tripods and Barrel Feet](/thumblibrary/U8611210/U8611210_01_140_140_Barrel-Foot-500-g.jpg)
![Electron Diffraction Tube S, 1013889 [U185711], Wave–Particle-Dualism](/thumblibrary/U185711/U185711_01_140_140_Electron-Diffraction-Tube-S.jpg)
![Digital Spectrometer LD, 1018103 [U22028], Spectrometers and Spectroscopes](/thumblibrary/U22028/U22028_01_140_140_Digital-Spectrometer-LD.jpg)
![Spectrum Tube – Hydrogen, 1003409 [U41817], Spectrum Tubes](/thumblibrary/U41817/U41817_01_140_140_Spectrum-Tube-Hydrogen.jpg)
![Optical Bench K, 1000 mm, 1009696 [U8475240], Optical System Kroencke – Accessories](/thumblibrary/U8475240/U8475240_01_140_140_Optical-Bench-K-1000-mm.jpg)
![Optical Lamp K, 1000863 [U8475400], Optical System Kroencke – Accessories](/thumblibrary/U8475400/U8475400_01_140_140_Optical-Lamp-K.jpg)
![Clamp K, 1008518 [U84755401], Optical System Kroencke – Accessories](/thumblibrary/U84755401/U84755401_01_140_140_Clamp-K.jpg)
![Converging Lens K, f = +50 mm, 1000869 [U8475901], Optical System Kroencke – Accessories](/thumblibrary/U8475901/U8475901_01_140_140_Converging-Lens-K-f-50-mm.jpg)
![Measurement / Control Unit – Franck-Hertz Experiment
(230 V, 50/60 Hz), 1012819 [U8482530-230], Franck-Hertz](/thumblibrary/U8482530-230/U8482530-230_01_140_140_Measurement-Control-Unit-Franck-Hertz-Experiment-230-V-5060-Hz.jpg)