Sample presentation for ``Rainbow Connection'' Pages refer to student worksheets 50-minute lesson Materials ------------------------------------------------------------ For each group: 5 LED/resistor combos (different colors, clear cases) battery pack voltmeter colored pens/pencils mystery LED(s) -- handed out later, if time allows For presenter: prism slide/overhead projector with slit 10-15 feet of flexible rope battery, LED, resistor, voltmeter setup to demonstrate overhead of circuit diagram and corresponding symbols overhead to draw graph on nonpermanent colored pens overhead of electromagnetic spectrum digital camera, if available PAGE 1 ---- (10 min) ------------------------------------------------- Introduce light as energy -- light is one type of energy -- brainstorm types of energy -- brainstorm how to change one type of energy into another White light is made of colors -- show rainbow with prism and light beam from slide/overhead projector (having a slit of light works best) -- note order of colors and have students record this in their worksheets for future reference What makes colors different? -- helps to know that light is a wave -- brainstorm waves (light, sound, water, stadium) -- introduce wavelength on blackboard -- different colors are actually different wavelengths How do you get different wavelengths? -- two student volunteers make waves -- compare waves when students move hands slowly, quickly -- compare the energy it takes to make short waves (lots) and long waves (not much) -- have students record this in their worksheets Light's wavelengths -- very short: less than the thickess of a human hair -- measure in nanometers, one billionth of a meter -- 1000 nanometers is hair thickness -- scientists can measure these wavelengths PAGE 2 ---- (10 min) --------------------------------------------------- Obtaining different colors -- use LEDs which are like tiny lightbulbs -- show one -- brainstorm where they've seen them (computers, car dashboards, flashing signs) -- depending on what material is inside, get a different color light -- clear case, unlike colored lightbulb Making a circuit -- concept of electrical circuit with ends attached all the way around -- show circuit diagram -- point out which parts are which -- battery supplies energy, LED gives off light energy, resistor uses up extra power -- explain +/- directions -- introduce multimeter by having students measure voltage of a battery, and compare to printed specs for that battery Give goals of experiment -- make a circuit out of each LED in turn -- measure the enrgy used using voltmeter -- write down wavelength of light from catalog Make graph when done -- draw data points in appropriate color (red for red LED, etc.) -- make a line to show the trend DATA TAKING ---- (20 min) -------------------------------------------- Allow students to take data for about 10 minutes, then make sure they start graphing whatever they have before taking more data. Students may need to join batteries with another group in order to get the blue LED to light up. Some extensions: -- have groups pair up and use the extra batteries so that the blue light bulbs light up all the way, and retake that measurement -- have students measure how many volts the resistor uses in each case PAGE 3/4 ----- (10 min) ----------------------------------------------- Discussion -- get one data point from each of several groups -- ask for general agreement on shape of graph -- ask if they recognize the order of the dots on the graph from the prism demo -- match waves and colors on page 4 of worksheet -- discuss how rope demo is related -- emphasize low energy = red, high energy = blue -- contrast to colors we associate with temperatures Mystery LEDs (infrared) -- hand out mystery LEDs -- have them do a measurement of energy at their desks -- discuss what the low energy says about the color -- show electromagnetic spectrum to show forms of light other than the visible -- have students identify some parts of the spectrum they recognize, and how they're used -- infrared is visible using a digital camera, if available Applying concepts -- star temperatures -- photosynthesis -- fireworks colors -- base vs. tip of a flame