![]() ![]() If you have space, you can go even farther, but remember that stray ambient light will affect your readings. Try to take measurements over a range of at least several meters.Take at least three readings at each distance and calculate an average.Measure the resistance of the photoresistor as you increase the distance from the lightbulb (for example, every 10 cm).In what other situations in physics does the inverse square law apply?.How do you expect the resistance to change as you move the photoresistor away from a light source (decreasing illuminance)?.How does the photoresistor's resistance change with increasing illuminance?.How is light measured in the metric system? What is the difference between intensity and illuminance?.Understand the following terms and concepts: To do this project, you should do research that enables you to You can then create a graph to see how illuminance changes with distance from the light source, and verify if it follows the inverse square law. Using information from the photoresistor's datasheet, you can convert the resistance measurement to lux, the SI unit of illuminance (a measure of intensity that accounts for how different wavelengths are perceived by the human eye). You will measure the resistance of the photoresistor at different distances from a light source. Image credit Wikimedia Commons user Borb.īut do not just take our word for it! Why not see for yourself if light really behaves this way? This project shows you how you can use a light-sensitive resistor, called a photoresistor, which has an electrical resistance (measured in ohms (Ω)) that changes with exposure to light, and a digital multimeter to see if light intensity really does decrease according to the inverse square law. An illustration of the inverse square law. The rate a light grows in area and decreases in brightness is related to the distance it travels from another point squared.įigure 1. The inverse square law shows that when light travels twice the distance its area grows four times as large and the brightness decreases by four times. As the light travels it has a specific brightness and size at any given point. The figure shows directional light originating from a point source that covers a larger area the further away it is from the source. ![]() 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/ r 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 farther, tripling the original distance ( 3r), and the light from the original square now covers an area of 9 (= 3 2) squares. Thus, at twice the original distance, the intensity (power per square meter) 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 ( 2r). Now imagine the light that falls on a square at some arbitrary distance from the star ( r). Imagine the light from the star spreading out into empty space in all directions. ![]() The blue area, marked "S," represents a point source of light. No doubt you have 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 |