See the Variations section if you want to test different types of bulbs. Make sure the bulbs you test are all the same type, for example, incandescent, compact fluorescent (CFL), or light-emitting diode (LED) and make sure they are all the same color (for example "warm white," "soft white," "cool white," or "daylight"). Light bulbs to test (at least 3 different wattages).Identical light fixtures, such as a clamp-on work lamp (2).Small cardboard box Note: the box that the paraffin wax comes in will work well.School Science Lessons: Physics: 2.2.4 Light Bulb Brightness, Joly Photometer. "The Parrot, the Pince-nez and the Pleochroic Halo," Europhysics News 32 (2). Since the numbers are calculated in proportion to the electrical signal, they are relative to the amount of electrical signal produced: the relative in the RLU. Note that you'll need to download the PDF of the document from the menu bar on the right-hand side of the page. To learn more about John Joly, the inventor of the Joly photometer, check out the article below. The wax blocks are mounted in a box with windows cut out on the left, front, and right sides, as shown in Figure 1.įor information on the inverse square law, see: In the Joly photometer, two equal-sized blocks of paraffin wax are separated by a layer of aluminum foil. As you'll see, the design of the photometer is based on the inverse square law. In this project you'll build a simple photometer, invented by the Irish scientist, John Joly. Because the same geometry applies to many other physical phenomena (sound, gravity, electrostatic interactions), the inverse square law has significance for many problems in physics. As you move away from a point light source, the intensity of the light is proportional to 1/ d 2, the inverse square of the distance. This is what is meant by the inverse square law. Thus, at three times the original distance, the intensity of the light passing through a single square will be 1/9 of the original intensity. Going out still further, tripling the original distance ( d = 3), and the light from the original square now covers an area of 9 (= 3 2) squares. Thus, at twice the original distance, the intensity of the light passing through a single square will be 1/4 of the original intensity. The light from the original square has now "spread out" over an area of 4 (= 2 2) squares. Move away, doubling the distance from the star ( d = 2). Now imagine the light that falls on a square at some arbitrary distance from the star ( d = 1, yellow square). Imagine the light from the star spreading out into empty space in all directions. At the center, the yellow star represents a point source of light. The diagram at right shows what is happening with a picture. No doubt you've noticed this with reading lamps, streetlights, and so on. As you move away from a light source, the light gets dimmer.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |