Name______________________________________ Period_______ Electromagnetic Spectrum Activity Objectives: explore several different types of light, both visible and invisible. Identify sources and detectors of various wavelengths of light Identify if various materials act as transmitters or shields for different types of light observe spectra produced by various light sources using a spectroscope Materials: One sheet of plain white paper Infrared light (assortment of remote controls) Camera phone Ultraviolet lamp Paper marked with Invisible ink Various materials that may act as transmitters that allow light to pass through or shields that block light Spectroscope Colored pencils PART 1- LIGHT SOURCES, DETECTORS, TRANSMITTERS, and SHIELDS Background: When most people hear the word “light”, they think of visible light that comes from the sun, a lamp, or a flashlight. What do we use as a detector to see that type of light? _____________ The electromagnetic (EM) spectrum is made up of all the different wavelengths of light, including visible and ranging from radio waves to gamma rays. Just as our ears can only hear certain frequencies of sound, our eyes can only see visible light, which makes up a tiny portion of the entire spectrum. Remember, scientists use the word “light” for any wavelength of energy, and will use the words ‘light’ and ‘energy’ interchangeably at time. Astronomical objects emit light at various wavelengths depending on their temperature. For example, the material around black holes is very hot and shines very brightly at X-ray wavelengths. Stars that are still forming are too cold to emit light at visible wavelengths, but do so at infrared (IR) wavelengths. Collecting data at different wavelengths is very important in astronomy, to gain a more complete picture. In this activity, you will be exploring different types of LIGHT. As you move through the three stations, you will use a variety of DETECTORS to observe different SOURCES of electromagnetic energy (light). You will also test different materials to determine whether they are TRANSMITTERS or SHIELDS for each wavelength of light. Modified from “Afterschool Universe Program Leader's Manual 35” Developed by the Lawrence Hall of Science with support from NASA’s Swift Mission http://universe.nasa.gov/afterschool/ PROCEDURE: Station 1 – Visible light SOURCE: Flashlight DETECTOR: Plain white paper and your eyes Shine the flashlight onto the white paper. Describe your observations: ___________________ _____________________________________________________________________________ _____________________________________________________________________________ Fill out the PREDICTION row for visible light on the chart on the next page. After you’ve made your predictions, TEST the various materials to determine if they are transmitters (T) or shields (S) for this wavelength of light. Mark each with a “T” or “S” on your chart. Station 2 - Infrared light SOURCE: Remote controls DETECTOR: Digital camera Look at the small bulb on the end of a remote control. When you push the buttons on the remote, what do you see? _______________________________________________________________ Now point the remote at the cell phone camera and push the buttons. What do you see on the camera screen? ________________________________________________________________ How do you explain these observations? ____________________________________________ ______________________________________________________________________________ ______________________________________________________________________________ Fill out the PREDICTION row for infrared (IR) light on the chart. After you’ve made your predictions, TEST the various materials to determine if they are transmitters (T) or shields (S) for this wavelength of light. Mark each with a “T” or “S” on your chart. Station 3 – Ultraviolet light SOURCE: Ultraviolet lamp DETECTORS: Paper with Invisible ink pattern Look at the white paper. Describe what you see. _____________________________________ Now shine the ultraviolet lamp on the paper. Describe what you see. ____________________ _____________________________________________________________________________ _____________________________________________________________________________ How do you explain these observations? *NOTE- even though you can see purple light from the UV lamp, this is not the invisible light that we are detecting. This is visible light that is too close to the UV light to be filtered out, but you should ignore it for this experiment. _________________________________________________________________________________ _________________________________________________________________________________ _________________________________________________________________________________ Fill out the PREDICTION row for Ultraviolet (UV) light on the chart. After you’ve made your predictions, TEST the various materials to determine if they are transmitters (T) or shields (S) for this wavelength of light. Mark each with a “T” or “S” on your chart. Write T if the material is a transmitter or S if it is a shield for each type of light. Clear Black Aluminum Paper Wax Plastic plastic Foil Paper Flashlight (visible) Blacklight (UV light) Remotes (IR light) Water Mirror Other? Prediction Result Prediction Result Prediction Result PART 2: SPECTROSCOPY Background: How do we know what the stars or the Sun are made of? The light of celestial objects contains much information hidden in its detailed color structure. Hot, glowing bodies like an incandescent light bulb or the Sun glow in all the colors of the spectrum. All these colors together appear as white light. When such white light hits a prism, or a raindrop, or a diffraction grating, colors get separated according to their wavelength. Red, with its wavelength of 600 nm to 700 nm, is deflected least and ends up on one edge of the spectrum – or the rainbow when sunlight hits a raindrop after a storm. Blue, wavelength around 400 nm, is the other end of the visible spectrum. An infinite number of elementary colors are located between these two edges, each corresponding to its own wavelength. An incandescent light bulb radiates a continuous spectrum. All colors are present in this “thermal glow”, and it is impossible to tell what the chemical composition of the source is. However, other physical processes produce different spectra. A fluorescent light tube works, crudely speaking, on the principle of lightening. Electrons rush from the negative pole to the positive pole inside, and hit gas atoms in the tube, making them emit light. This sort of light contains only a few colors, and is called “emission spectrum”. When we separate the colors of such light, only a few bright “emission” lines appear, each in its own color (and wavelength). Each sort of an atom will emit light at its own particular set of wavelengths. When we analyze the emission spectrum of an unknown source, we can compare the colors of its spectral lines to known spectral lines we see in a laboratory, and tell which substance matches. PROCEDURE: You will be using spectroscopes to observe the spectra produced by a variety of visible light sources. Aim the small slit on the side of the wide end of the spectroscope directly at the light. You should see the spectrum on the right when you look through the narrow end. Use the colored pencils to illustrate your observations on the scales below. The numbers on the scale represent 1000 angstrom (Å) or 100 nanometers (nm) Incandescent light bulb- An incandescent bulb uses heat caused by an electrical current. When electrical current passes through a wire, it causes the wire to heat. The wire, or filament, gets so hot that it glows and gives off light. Everyday incandescent light bulbs have a filament made of tungsten. 4 5 6 7 CFL desk lamp – CFLs (compact fluorescent light) produce light differently than incandescent bulbs. In a CFL, an electric current is driven through a tube containing argon and a small amount of mercury vapor. This generates invisible ultraviolet light that excites a fluorescent coating (called phosphor) on the inside of the tube, which then emits visible light. 4 5 6 7 LED nightlight --LEDs (light-emitting diodes) emit light from a piece of solid semiconductor. An LED produces light when electrons move around within its semiconductor structure. The positive layer has "holes" -- openings for electrons; the negative layer has free electrons floating around in it. When an electric charge strikes the semiconductor, it activates the flow of electrons from the negative to the positive layer. Those excited electrons emit light as they flow into the positively charged holes. 4 5 6 7 Laptop computer screen (LCD - liquid crystal display) 4 5 6 7 4 5 6 7 4 5 6 7 Whiteboard- Red light bulb- ANALYSIS QUESTIONS: Part 1: Why did you need to use different detectors for the different types of light? Were there materials that were transmitters for some types of light but shields for other types? If so, explain: What observation was most interesting or surprising to you? Explain… Part 2: What were some of the similarities you noticed between the different spectra? What were some of the differences you noticed between the different spectra? Does the whiteboard emit light? Why do you see a spectrum when you point your spectroscope at the whiteboard?