Astronomy 102 Name(s): Lab 2: The electromagnetic spectrum Purpose: In this lab, you will explore the phenomenon of light, and see that the electromagnetic spectrum provides a comprehensive model for understanding all forms of light, including invisible light. Further, you will use various equipment to detect the invisible portions of the spectrum. Each part of the lab will list the equipment necessary. The model of the electromagnetic spectrum is presented above. 1. Given that the spectrum is organized by wavelength, light is a wave phenomenon; in other words, light travels across space like a wave. So what do the units mm, µm, nm and pm stand for? Convert each prefix into the appropriate scientific notation number. 2. Label the appropriate ends of the spectrum as short or long. 3. Energy (the ability to move) is transmitted by light (= electromagnetic waves). The energy may be calculated by using the formula E =!!, where E is the energy of the wave in joules (J), h is a number called Planck s constant = 6.626 10 34 Js (Joule-seconds), c is the speed of light = 3.00 10 8 m/s and λ is the wavelength of the light wave, measured in meters (m). Perform the calculation to fill in the table below: Color of light Wavelength (nm) Energy (J) Red 700! Violet 400
4. Note that the energy of invisible waves may be calculated in the same fashion. Label the appropriate ends of the spectrum as high energy waves or low energy waves. Needed: The sodium lamp, an alcohol lamp, a crystal of sodium chloride salt, tongs, white light source, diffuser 5. Turn on the sodium lamp, set up the diffuser screen in front of it, and note the color that you see. Compare this color to the sodium emission shown on the chart in the classroom; what wavelength (in nm) is most likely the source of the color you see? 6. Set up the white light source behind the diffuser, next to the sodium lamp. Then set up the alcohol lamp in front of the screen. The instructor will hold a sodium chloride crystal in the alcohol lamp flame, such that the crystal is in the line of sight between you and the sodium lamp. What do you see? Why is this happening? Compare it against the white light background to prove you aren t just seeing things. Hint: The sodium lamp is the source and the salt crystal in the flame is the sample. 7. Using the energy level diagrams from the textbook, explain on the atomic electronic level what is happening with the light of the sodium lamp and flame.
Needed: Infrared camera, fog/smoke machine, opaque trash bag, transparent plastic bag, glass The astronomer William Herschel published his discovery of beyond red infrared (IR) light in 1800 at the Royal Society of London. Many years later, researchers at various companies found that an alloy of the metals cadmium, tellurium and mercury would absorb long-wave infrared light, which then can be used as a camera. 8. Set up the IR camera such that it projects onto the screen, then turn on the fog/smoke machine. The instructor will pan the camera across the classroom (ideally, you cannot see the camera). Are you visible to the camera? Does the smoke/fog block IR light? What is the camera actually seeing? 9. How is this related to Wien s Law (use your body temperature of 310 K)? 10. Place the trash bag over the instructor s head and pan the camera at the instructor. Is the instructor s head still visible? Does the particular plastic of the trash bag block IR light? Try other materials; what transparent material blocks IR light?
Needed: Ultraviolet light box with long wave and short wave UV, UVA sensor, Vernier LabQuest datalogger In 1801, Johann Ritter, a German physicist, observed light beyond violet ultraviolet (UV) rays by exposing silver salts that darkened as a result of absorbing UV radiation. Many years later, researchers invented a silicon photodiode to do much the same thing. 11. Plug the UVA sensor into the datalogger and make sure the display shows a reading. Point the sensor at the UV light, taking care to not expose yourself to the UV light, and record the measurement in the table below. Also record the wavelength of light the UV light is emitting; do the same for the other wavelength that the UV light emits. Wavelength of ultraviolet light emitted (nm) Reading from UVA sensor (units?) 12. While getting a positive reading on the datalogger from either of the sensors, place various transparent items between the UV light and the sensor to see what material will absorb the UV light. How can you tell if the UV light is absorbed by a material? 13. What material absorbs UV light? How is this applicable to your life?
Needed: Cheap transistor radio, wire mesh Physicist Heinrich Hertz, in 1887, experimentally demonstrated the existence of yet another form of light, which was eventually called radio waves. Early radio detectors used a quartz crystal, called an oscillator, to absorb radio waves. Currently, there are many ways (and materials) that detect radio waves. 14. On the radio, find and record the units of the numbers on the dial for both AM and FM wavebands. These are units of frequency. These units are related to wavelength in a simple way: wavelength (in meters) = (speed of light)/(frequency). 15. Turn on the radio and find a relatively strong station. Note the frequency and the units of the station in the table below. Switch wavebands (AM to FM, or vice versa). Find another strong station and note its frequency. Note the frequency and the units for this station; calculate the wavelength of each station. Waveband Frequency of radio station (show appropriate units) Wavelength of radio station (m) What happens when mesh is placed around radio AM FM 16. Place the mesh around the radio and find the two stations, then note how strong their signals are, compared to before. The mesh is called a Faraday cage. What does the Faraday cage appear to do to AM radio waves? There is a much more complicated reason why it does not affect FM radio waves.
Needed: The plasma ball, fluorescent light tube, other materials as needed The plasma ball is a small version of the Tesla coil, an invention of Nikola Tesla, a Serbian-American engineer, who, in 1891, envisioned it as a way to deliver electricity. 17. Turn on the plasma ball. Obviously, what part of the EM spectrum is being emitted (ignore the sound)? What happens when the fluorescent light tube is brought close to the plasma ball? Does the tube have to touch the surface of the bulb for this to occur? What is being transferred from the plasma ball to the fluorescent tube? 18. Place an opaque material between the plasma ball and the fluorescent tube. Does this interrupt the lighting of the fluorescent tube? Is visible light from the plasma ball lighting the fluorescent tube? 19. Place the other materials that we have previously used to block various EM waves and write the results of these experiments below. Does any material prevent the fluorescent tube from lighting up? If so, what type of EM radiation is performing the energy transfer? 20. To confirm your hypothesis about the type of EM radiation involved, what happens when you place the transistor radio near the plasma ball? How does this observation help determine what part of the spectrum is involved in the energy transfer between the ball and the tube?