![]() ![]() See NZSMT Teacher Fellowships for more information about the Teacher Fellow Program. Rory is a science teacher by training and was Deputy Principal at Lytton High School in Gisborne, New Zealand. This teaching resource was developed in collaboration with Rory O’Keeffe, a New Zealand Science, Mathematics and Technology Teacher Fellow, 2007, hosted by Victoria University School of Chemical and Physical Sciences. Would you like to contribute lesson suggestions? Contact us. Through the looking glass Teaching Resources Even familiar demonstrations should be practised and safety-checked by individual teachers before they are used in a classroom. Individual teachers are responsible for safety in their own classes. SafetyĪvoid looking at the sun, lasers, or other bright sources. Note: to improve results, you can put a cardboard slit in front of the light sources but be very careful not to let the cardboard get too close to the bulbs, particularly the incandescent as it will be very hot. As you increase the temperature, making the filament hotter, all of the colours get brighter but the percentage of light in the blue and violet increases dramatically as expected for something approximating a blackbody. When the filament is warm blue and violet are pretty much missing. Or put an old incandescent bulb on a dimmer to illustrate colour temperature and blackbody radiation. With the compact fluorescent bulb you can see the visible part of the Hg bar code and the light produced by fluorescence, and the the LED you can see the driving light (far blue/violet), a fluorescence gap, and the fluorescence spectrum. Have a look at a compact fluorescent bulb and an LED bulb. Glowsticks LTD sell throughout New Zealand. These glasses are invaluable for investigating modern lighting technology. GloFX designs and manufactures products including Diffraction Glasses, Kaleidoscope Glasses, Rave Goggles. With this number in hand you can measure the wavelength of other lines in other spectra. Results agree well with the 500 lines/mm given on the glasses. The separation of the source from one of the observed D lines can be used to calculate sin θ in the formula The distance from the source is recorded. Looking at the discharge tube through the glasses students walk away from the source until the perceived D lines line up with the two marks. Mark two points about 3 m apart and place the sodium discharge tube in the centre. For example, the bright sodium D line (589 nm) can be used to calculate the actual spacing of the glasses. Examples are displayed below.Īlthough a qualitative demonstration with these glasses is enormously useful in itself, quantitative measurements can be made as well. Increasing the distance between the observer and the light source will spread out the observed spectrum. The images above do not do justice to the visual observations. If possible face the light sources away from each other to prevent stray light affecting the observed spectra. The tubes will need to be covered so that only a small slit of light is exposed. These glasses are very inexpensive and are very useful. It is possible to do pretty good quantitative experiments with these glasses. This can be used to illustrate everything from “bar codes” for chemical elements to colour temperature to lighting technology and so on. The diffraction gratings separate the colours contained in a light source. The “bar code” for neon as seen through the glasses Portable A biconvex lens is called a converging lens.Inexpensive diffraction grating glasses are used to observe the spectra of many light sources. Parallel rays of light can be focused in to a focal point. This is the kind of lens used for a magnifying glass. There are two kinds of lens.Ī biconvex lens is thicker at the middle than it is at the edges. LensesĪ lens is simply a curved block of glass or plastic. The light bends away from the normal line.Ī higher refractive index shows that light will slow down and change direction more as it enters the substance. If light travels enters into a substance with a lower refractive index (such as from water into air) it speeds up. If light enters any substance with a higher refractive index (such as from air into glass) it slows down. Refractive index of some transparent substancesĪll angles are measured from an imaginary line drawn at 90° to the surface of the two substances This line is drawn as a dotted line and is called the normal. On the other hand, if the light is entering the new substance from straight on (at 90° to the surface), the light will still slow down, but it won’t change direction at all. Angle of the incident ray – if the light is entering the substance at a greater angle, the amount of refraction will also be more noticeable.Change in speed – if a substance causes the light to speed up or slow down more, it will refract (bend) more.The amount of bending depends on two things: ![]()
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