31 Mar, 2013
PRESENTATION: The refractive index of a medium decreases as the wavelength increases. This means that the longer visible wavelengths of light (red) are shifted less than the shorter ones (blue) to produce a dispersion phenomenon that is commonly seen in everyday life as a rainbow, which is produced when light is dispersed by raindrops in the atmosphere.
- RAINBOW, Paul Hewitt, Phys. Teach. 44, 268 (2006)
- Why is white light dispersed by a prism?, Frank S. Crawford, Phys. Teach. 17, 583 (1979)
INTRODUCTION: The rainbow is an optical phenomenon that makes a continual spectrum of light frequencies appears as light rays pass through water droplets. There are many ways to observe this event. They include: spray water on a sunny day; put a mirror on a tray full of water and then place a sheet of white paper in front of it; or look out for the meteorological phenomenon itself.
OBJECTIVE: To show that light, when it is reflected and refracted in a glass bottle full of water, produces a separation of the light to give rise to a rainbow.
MATERIALS: Cylindrical glass bottle, focusable flashlight, sheet of white paper, water.
SETUP: Fill the glass bottle with water and place it in a dark room. Put the sheet of white paper under it to get the best results. Use the flashlight to make a beam hit the surface until you find the angle at which the light is split to form the frequency spectrum.
EXPLANATION: When the beam of light hits the water in the bottle, the yellow light is diverted by 138º with respect to the angle of entry. This angle is smaller for some other colours (red) and greater for others (violet). First, the ray of light enters the water and is slightly refracted before being reflected on the internal surface of the bottle. Finally, it is refracted again when it leaves the liquid as dispersed light. This is because the refractive angle is different for each wavelength.
CONCEPTS: reflection, refraction, frequency, light.
- YOUTUBE 1
- YOUTUBE 2
- YOUTUBE 3
- YOUTUBE 4
- YOUTUBE 5
- YOUTUBE 6
- YOUTUBE 7
- UNIVERSITY OF TEXAS
- NORTHWESTERN UNIVERSITY
- DUKE UNIVERSITY
- R. Serway, Física, Mac Graw Hill, 2010.
- P. Tipler, Física para la Ciencia y la tecnología, Reverté, 2012.
- R. Ehrlich, Turning the World Inside Out and 174 Other Simple Physics Demonstrations, Princeton University Press, 1997.
STUDENTS 2011-2012: Carlos Coroas, María Cotón, Alejandro Vidal, Luís Rodríguez
LINK pdf STUDENTS (In Galician):
STUDENTS 2011-2012: Pablo Pallas, Alejandro Paz, Raquel Pérez
LINK pdf STUDENTS (In Spanish):