1000 6B10.20 inverse square with photocell L-11 Double and triple the distance from an arc source to a photocell connected to a galvanometer. 6B10.20 inverse square law Disc 21-10 Double and triple the distance between a source and photometer. Two large paraffin blocks with tin foil sandwiched in between make a sensitive photometer. Use with lamps on either side. Two paraffin blocks separated by an aluminum sheet are moved between two light sources until they appear equally bright.
Tin foil is sandwiched between two blocks of paraffin.
Can be mounted in a box for greater accuracy. Oi-3 A piece of paper with a grease spot is moved between two light sources until the spot disappears. A grease spot disappears when illuminated equally from both sides. Diagram of a grease-spot box. Light sources are moved until their shadows of the same object are of equal intensity.