Optical Obstacle Course

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 50 cm apart, and the light will be partly collimated into a beam approximately 20 mm wide, centred 40 mm above the table.  It will be adjusted to maximize the light hitting the sensor and that value will be recorded as the total light available.  Then a cylindrical object will be placed at the centre of the path to block the light.  It is 12.85 cm tall, with a radius of 7.78 cm and diameter of 15.56 cm.  You will have 5 minutes to install your device to direct as much light as possible around the obstacle and back to the photosensor.  Your device must not touch the obstacle and may not exceed a radius of 20 cm from the centre of the obstacle.  The build area must remain inside an imaginary cylinder of diameter 40 cm and height of 30 cm. You must use at least one plane mirror, one curved mirror (concave or convex), one rectangular prism (a piece of plate glass would count), one angled prism (if you take advantage of internal reflection, then this can count as your plane mirror as well), one convex lens, and one concave lens.  You can use as many more elements 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.  Early elements can be used to divide the light into two or more paths, each of which must be no less than 10% of the overall light intensity.  Each path must have at least 50% unique elements, and be easily obstructed to allow for measurement or calculation of their contribution to the overall light intensity.

Scoring:  Score = (Illuminance Ratio) • (P)

Where Illuminance Ratio is the amount of light getting the the photosensor compared to the total light available, and P is the number of distinct paths (of minimum 10% of the total light intensity) taken by the light from the LED to the photometer (up to a maximum of four).

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. 10% of intensity) taken.  You also need a detailed scale 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 boundaries 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:  A light beam can be split into two paths with careful placement of a mirror or prism.  Actual beam splitters can be made from mirrors by very carefully sanding off the backing metal and testing relative intensity of the two beam fractions at 45°, but this takes a lot of patience to avoid scratching the glass face!

Help/Hints:  Each boundary encountered by the light will cause some energy to be lost.  Adding another path can increase your score, but only if you can still get most of the light to the sensor!

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)