Electromagnetic Radiation Practice Problems What is Electromagnetic Radiation? Classwork c = λf c = 300,000,000 m/s
time (s) = distance (m)/ speed (m/s)
1. 2. 3. 4. 5.
What are some sources of electromagnetic radiation? What is meant by the term “medium”? Why can electromagnetic waves travel through a vacuum? What speed do all electromagnetic waves travel at in vacuum? Red light, a type of electromagnetic wave, has a wavelength of 0.0000078 meters, what is its frequency in Hz? 6. Most kitchen microwaves operate at a frequency of 2,450 MHz or 2,450,000,000 Hz. What is the wavelength of these microwaves? 7. Alpha Centauri is the nearest star to Earth at 41,342,509,100,000,000 meters away. How long would it take a radio signal – a type of electromagnetic wave – from Alpha Centauri to reach Earth? 8. TV channels 5 and 6 broadcast frequencies between 76 and 88 MHz. What is the wavelength of a 76 MHz frequency? Homework 9. What do X-rays, light, microwaves, and radio waves all have in common? 10. All electromagnetic waves travel at what speed in a vacuum? 11. What is a vacuum? 12. When electromagnetic waves travel through matter, what happens to their speed? 13. Which of the following electromagnetic waves has the highest frequency: 1.0 m wavelength, 100 m wavelength, 0.001 m wavelength, or 1,0000 m wavelength? 14. How does the frequency of an electromagnetic wave with a long wavelength compare to the frequency of an electromagnetic wave with a short wavelength? The Electromagnetic Spectrum Classwork 15. What does the term “spectrum” mean? 16. What happens to the energy of a wave as the frequency of a wave increases? 17. What happens to the energy of a wave as the wavelength of a wave increases? 18. What form of electromagnetic wave has the highest energy? 19. What form of electromagnetic wave has the lowest energy? 20. Rank the following forms of electromagnetic radiation in order of increasing energy: Infrared Waves, Radio Waves, X-Rays 21. Rank the following forms of electromagnetic radiation in order of increasing energy: Gamma Rays, Microwaves, Ultraviolet Homework 22. In order for a radio to work, what two items are needed? www.njctl.org
8th Grade PSI
Electromagnetic Radiation
23. What are 5 ways microwaves are used? 24. What are the three major categories of light electromagnetic radiation? 25. Rank the following in order from longest to shortest wavelength: red light, infrared, ultraviolet, and violet light. 26. What does the acronym ROYGBIV stand for and what is its purpose? 27. What are the two highest energy types of electromagnetic radiation and what are they used for? Light Interactions with Matter Classwork 28. What is the imaginary line perpendicular to the surface of a material called? 29. The angle between the incoming light and the line asked for in #28 is called what? 30. What is the angle between the reflected light and the line in #28 called? 31. What is the relationship between the two angles in #29 and #30? 32. What is another term for the bending of light? 33. In order for light to refract what two conditions must be met? 34. If light enters a denser material from one that is less dense, how will the light behave? 35. If light enters a less dense material from one that is denser, how will the light behave? Homework 36. Based on the diagram below, which substance is denser? How do you know
37. When light enters a substance with a different density, what is the angle of reflection? 38. How does the angle of refraction for light with a higher frequency compare to that of a lower frequency light? 39. How does the angle of refraction compare for red and violet light passing through the same object? Explain. 40. If a light passes from air, through glass, and back into air, how does the angle of refraction from glass to air compare to the angle of incidence from air to glass? www.njctl.org
8th Grade PSI
Electromagnetic Radiation
Answers 1. The Sun, radon gas, nuclear reactions, and light bulbs. 2. A medium is a substance 3. Electromagnetic waves can travel through a vacuum because they don’t need a medium to travel through. 4. 300,000,000 m/s 5. 38,500,000,000,000 Hz 6. 0.12 m 7. 1.37 x 108 or 5,700,000 days or 15 years. 8. Around 3.9 m. 9. They are all types of electromagnetic radiation. 10. 300,000,000 m/s 11. A vacuum is a region of empty space devoid of any matter. 12. When electromagnetic waves travel through a medium they slow down. 13. 0.001 m wavelength 14. Electromagnetic waves with long wavelengths have low frequency and electromagnetic waves with short wavelengths have high frequency. 15. Spectrum means a continuous range 16. The energy increases as the frequency increases 17. The energy decreases as the wavelength increases 18. Gamma Radiation has the highest energy. 19. Radio waves have the lowest energy. 20. Radio < Infrared < X-ray 21. UV
8th Grade PSI
Electromagnetic Radiation
35. If light enters a less dense material from one that is denser, it bends away from the normal. 36. The oil is the densest because the angle of refraction is the steepest or most bent toward the normal. 37. When light enters a substance with a different density, the angle of reflection is the same as the angle of incidence. 38. Light with a higher frequency has a shorter wavelength and greater angle of refraction. 39. Violet light has a greater angle of refraction than red light because red light has a longer wavelength. 40. If a light passes from air, through glass, and back into air, the angle of refraction from glass to air is equal to the angle of incidence from the air to glass because the frequency of the light is unchanged and the velocity of the original incident light in air is equal to the velocity of the refracted light in air, so as the light passes from glass to air it returns to its original velocity and, therefore, original angle of incidence.
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8th Grade PSI
Electromagnetic Radiation
