06 Mar, 2013
PRESENTATION: When light is incident on a surface that separates two refractive media, the reflected light is partially polarised and the degree of polarisation depends on the angle of incidence and the refractive indices of both materials. For an incidence with Brewster’s angle, the light is totally polarised in a plane perpendicular to the plane of incidence.
- Experiencing Light’s Properties Within Your Own Eye, Michael Mauser, Phys. Teach. 49, 19 (2011)
- Real 3-D: How Does It Work?, H. Schmitzer, D. Tierney, and T. Toepker, Phys. Teach. 47, 456 (2009)
INTRODUCTION: In a non-polarised wave, the vibration oscillates in all possible directions perpendicular to the direction of propagation. Starting from this state, the wave is polarised if for some reason it starts, for example, to oscillate on just one particular plane, which is called the polarisation plane.
OBJECTIVE: To verify the variation in the intensity of the reflection by placing and turning the polariser between the light and the screen.
MATERIALS: laser or light beam, piece of glass, polariser.
SETUP: The glass is placed on a table or any other support. Switch on the laser and aim it at the glass at an angle of 56º with respect to the horizontal. In this way, part of the light is reflected at an angle of 36º and the laser is focused towards a wall. Finally, the polariser is placed between the glass and the wall so that the ray of light goes through it. When the polariser is turned the reflection on the wall is reduced in intensity.
EXPLANATION: When unpolarised light is reflected on a flat surface between two transparent media, for example, that which separates air and glass, the reflected light is partially polarised. The degree of polarisation depends on the angle of incidence and the refractive indices of both media. The electric field of the incident light can be broken down into two components, one parallel and one perpendicular to the plane of incidence. The reflected light is completely polarised with its vector of the electric field perpendicular to the plane of incidence. The reflected light is totally polarised in a plane when the angle complies with Brewster’s law . The refracted light is partially polarised and much more intense than the reflected light. For angles that are not polarisation angles, the reflected light and the refracted light are partially polarised.
CONCEPTS: Brewster’s angle, Brewster’s law, reflection, refraction, refractive index.
- P.A. Tipler, Física, Reverté, 2010.
- S. Burbano de Ercilla, C. García Muñoz, Física General, Tebar, 2008.
- F.S. Crawford, Ondas, Reverté, 2005.
- R. Ehrlich, Turning the World Inside Out and 174 Other Simple Physics Demonstrations, Princeton University Press, 1997.
STUDENTS 2010-2011: Antonio Dacosta, Alberto Díaz
LINK pdf STUDENTS (in Spanish):