Name: Unit 5- Light and Energy Electromagnetic Spectrum Notes Electromagnetic radiation is a form of energy that emits wave-like behavior as it travels through space. Amplitude (a)- Wavelength (λ)- Which of the following has a higher frequency? Frequency (ν)- Electromagnetic radiation can be displayed in the electromagnetic spectrum. This spectrum places all of the wave types in order based on wavelength (λ) and frequency (ν). 1
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Light and Energy Notes In 1900 Max Planck helped us move toward a better understanding of electromagnetic radiation. o Matter can gain or lose energy only in small, specific amounts called quanta. o A is the minimum amount of energy that can be gained or lost by an atom. Light and energy can't always be explained using waves. In 1905 Albert Einstein proposed that electromagnetic radiation has both wavelike and like natures. o In the photoelectric effect electrons (or photoelectrons) are emitted from a metal's surface when light or energy of a specific frequency comes in contact with the metal. While a beam of light has many wavelike characteristics, the beam can also be thought of as a stream of tiny particles or bundles of energy called photons. A is a particle of electromagnetic radiation with no rest mass that carries a quantum of energy. Louis de Broglie (1892-1987) o Only whole numbers of wavelengths are allowed in a circular orbit of a fixed radius o Light has characteristics of both waves and particles o Electrons move in wavelike motion with restricted circular orbits Niels Bohr (1885-1962) o Proposed a quantum model o Predicted frequencies of hydrogen's atomic emission spectrum o He said atoms have only certain allowable energy states o Related energy states to the motion of electrons in circular orbits 3
By passing light through an elemental gas, the atoms absorb energy and an electron will move to a higher energy level (farther away from the nucleus). The atom is then said to be in an. This energy is then released in the form of light when the electron falls back to the ground state. The farther the electron has to fall, the energy is released and the lower the wavelength of light is emitted. When passed through a prism this light is then seen as an atomic emission spectrum or a series of colored lines which correspond to a series of frequencies of the electromagnetic waves emitted by that element. 4
Light and Energy Worksheet Answer all questions in complete sentences. 1. Define photon. 2. According to debroglie, how do electrons move? 3. Draw a picture of Bohr s atomic model. Label n = 1 n = 4 and indicate the ground state. 4. What colors are present in white light? 5. List the colors of the visible spectrum in order of increasing energy. The photons of which type of visible light would carry the greatest frequency? 6. What type of visible light has more energy, blue light or orange light? 7. Which type of electromagnetic radiation would be more harmful to humans: microwaves or gamma rays? Explain. 8. Put the following in order from lowest frequency to highest frequency: UV light, Radio waves, infrared and visible light. 5
9. Which form of electromagnetic radiation would reach Earth faster if both forms were emitted simultaneously from a probe in space: X-rays or gamma rays? Explain. 10. Which photons would have a greater amount of energy: a photons with a wavelength of 125 nm or a wavelength of 3456 pm? 11. Draw a wave and label it with the three characteristic properties of all waves and explain what is meant by each. What units are used to measure λ and ν? 12. Explain the relationship between the frequency and wavelength of a photon. 13. Radio stations can broadcast in an AM frequency or an FM frequency. A popular AM station in Washington is broadcast at 980 khz (it broadcasts Redskins games) and a popular FM station broadcasts at 97.1 MHz. Which ration station broadcasts with a longer wavelength? 14. Explain what is meant by a quantum of energy. 15. UV A and UV B rays will give you a sunburn. If the wavelength emitted by a photon classified as UV-A light is 380nm and the wavelength emitted by a photon is classified as UV-B is 313 nm, which rays are responsible for the worse sunburn? Explain. 6
Light and Energy Calculation Notes All electromagnetic waves travel at the same speed in a. This speed (c) is 3.00 x 10 8 m/s in a vacuum. o c is more commonly referred to as the. c = λν c = speed of light, 3.00*10 8 m/s λ = wavelength ν = frequency What is the frequency of light with a wavelength of 380. nm? What is the wavelength of light with a frequency of 98.6 khz? E = hν E = energy h = Planck's Constant, 6.626*10-34 Js ν = frequency What is the energy of light with a frequency of 1430 MHz? What is the frequency of light with an energy of 3.40*10-19 J? 7
Wavelength and Frequency Worksheet 1. What is the wavelength of a photon with a frequency of 4.5 x 10 16 Hz. 2. What is the wavelength associated with a frequency of the radio station 91.9MHz? 3 A laser used in eye surgery to fuse detached retinas produces radiation with a frequency of 4.69 x 10 14 Hz. What is the wavelength associated with this frequency? 4. What is the frequency of light with a wavelength of 360nm? 5. What is the frequency of light with a wavelength of 2.32 pm? 8
Energy Worksheet 1. What is the energy associated with light that has a frequency of 97.1 khz? 2. Calculate the frequency of a photon with an energy of 2.3 x 10-22 J. 3 A laser used in eye surgery to fuse detached retinas produces radiation with a frequency of 4.69 x 10 14 Hz. What is the energy associated with this frequency? 4. What is the energy associated with light with a wavelength of 457nm? 5. What is the energy of a photon with a wavelength of 345 nm? 6. Calculate the wavelength of light with an energy of 4.42*10-19 J. What color is this light? 9
Unit 5 Quiz Review You must memorize Speed of Light AND Planck s Constant. 1. For each pair, determine which has the lowest energy, highest frequency, and longest wavelength. X-ray / Microwave Orange light / Violet light Radiowaves /Gamma Rays Low Energy: Low Energy: Low Energy: High ν: High ν: High ν: Long λ: Long λ: Long λ: 2. Draw a picture of the Bohr model, label the ground state and give the major failing of the model, then explain what happens within an atom when we see light being emitted. 3. List the electromagnetic spectrum in order of decreasing energy. 4. Discuss the contributions of Neils Bohr. 5. Discuss the contributions of Max Planck. 6. Discuss the contributions of Louis debroglie. 7. Define photon. 8. Indicate which of the following drops would release ultraviolet light and why. n = 2 n = 1 n = 4 n = 2 n = 6 n = 4 10
Calculations: 9. What is the frequency of light with a wavelength of 5.7*10-7 m? 10. What is the wavelength of a radiowave with a frequency of 87.9 MHz? 11. What is the energy of a photon with a frequency of 53.2 khz? 12. What is the frequency of a photon with an energy of 6.39*10-15 J? 13. What is the energy of a photon with a wavelength of 7.53 pm? 14. What is the energy of a photon with a wavelength of 345 nm? 15. A laser used in eye surgery to fuse detached retinas produces radiation with a frequency of 4.69 x 10 14 Hz. What is the wavelength associated with this frequency? 16. What is the energy associated with the frequency in problem 15? 17. Calculate the energy associated with yellow light with a wavelength of 589nm. 11