Prism Refraction-Wave and Dipole Picture Please click the link below for a description of the graphics. Refraction by a prism is a more advanced version of the previous refraction by a slab simulation because the angle of the incident interface differs from that of the exiting interface. In this simulation we will simplify this angle difference by choosing to have the incident and the exiting angles the same. This symmetric orientation is called the "Angle of Minimum Deviation". The incident angle, thetaI, for this situation is computed as sin(thetaI)=n*sin(thetaP/2) where n is the index of refraction of the prism and thetaP is the vertex angle of the prism. Of course the product n*sin(thetaP/2) may sometimes exceed 1.0, which would make thetaI invalid, so that, if the learner chooses either thetatP or n so that this occurs, the program automatically reduces the other parameter and provides a red message to the learner that it has done so. One major goal of this simulation is to show how the phase of the wave is continous at both indident and exiting interfaces of the prism. Another goal of the simulation is to show how the dipole phasing (red/black) is synchronous with the wave in the prism. It is very important that the learner understand that an electromagnetic wave has its electric field perpendicular to its direction of propagation (i.e. it is a TRANSVERSE WAVE). That is the main guiding principle of any refraction demonstration. Because of this,the number of waves between the starting plane and the ending plane, for all three rays shown, are the same. To convince the learner of this I have printed the number of eace wave between starting and ending plane. For a treatise on the math at prism angles other than that of minimum deviation, please click the Prism Math link below.
Click here for Prism Math Click here Graphics Description psiV thetaP