Challenge: To build a structure comprised of several optical devices that will maximize the amount of LED light energy that can travel to a photosensor.
Parameters: The photometer and LED will be separated by approximately 28 cm. The build area must remain inside an imaginary rectangular prism whose length matches a piece of standard paper, and whose width and height match the width of a regular piece of paper. You will build the LED circuit on a breadboard. The LED will need to be adjustable up to 25 mA. You may not exceed 25 mA. You must use at least one mirror, one lens, and one prism, but can use as many more as you wish. All optical elements used must be in the allowed area, and must be part of an identifiable light pathway or they will not be counted towards your score. An element can divide the LED light into two or more paths, each of which must be no less than 5% of the overall light intensity. Each path must have at least 50% unique elements, and be easily removed or obstructed to allow for measurement or calculation of their contribution to the overall light intensity.
Scoring: Your system will be scored based on the amount of light energy reaching the photometer, the number of distinct paths to the photometer, and the number and variety of optical devices used in the light path(s).
Score = (Illuminance in Lux / 200 Lux) • (P) • (T)0.5 • (N)0.333
Where P is the number of distinct paths (of minimum 5% of the total light intensity) taken by the light from the LED to the photometer (up to a maximum of four), T is the number of different types of optical elements (up to a maximum of 16) and N is the total number of optical devices used, up to a maximum of 27.
Your journals MUST include a large, detailed diagram drawn to scale for your setup, with a key identifying each optical element, and the distinct paths (min. 5% of intensity) taken.
Your journals need a detailed ray diagram of the physics happening for each optical element used, for each of the paths you have identified.
Physics: Waves can transmit and reflect at boundaries. Some media will cause the energy of the light to dissipate or scatter from the intended path. Curved devices may converge or diverge the light energy. The angle of plane mirrors, and the focal length and placement of curved elements (mirrors or lenses) is crucial to the success of your project. Also note that the higher the angle of incidence, the greater the proportion of reflection relative to transmission.
Extensions: The photometer is most sensitive to 550 nm light. Why might that be the case?
The physics of diffraction gratings can be extremely interesting, and it is how the counterfeit counter-measure of the modern Canadian bills works.
Help/Hints: Each boundary encountered by the light will cause some energy to be lost. Can you think of a way to have more optical devices without increasing the number of boundaries encountered?
Quiz Topics: Light as a quantum particle (photon), Light as a wave, Light as a ray, Lenses, Mirrors, Refraction, Reflection, Dispersion, Scattering, Diffraction, Interference
Online Text: 13 (Light as a Wave), 15 (Electromagnetic Spectrum), 16 (Lenses), 17 (Interference), 21 (Quantum Theory of Light)