Unit 56: Electromagnetic Radiation
Practice Problems
Note: problem difficulty is ranked using a star system.
(*) One-star problems are fundamental to the unit, and can be done relatively quickly. Use these problems to introduce yourself to the material.
(**) Two-star problems are more difficult, and require an understanding of one or two key concepts. Use these problems to test your understanding of the material.
(***) Three-star problems are the most difficult, and require some creative thinking in addition to a deep familiarity with multiple key concepts. Use these problems to challenge yourself; if you can complete one of these, you’re on your way to mastering the material.
*Q56.1) Consider the following types of electromagnetic radiation: red light, blue light, green light, ultraviolet, infrared, microwaves, x-rays, radio waves, and gamma rays.
a) Arrange them in order of decreasing wavelength.
b) Arrange them in order of decreasing frequency
c) Arrange them in order of decreasing energy per photon.
**Q56.6) The Sun emits light with a peak wavelength of 550nm (green light), while the Earth emits photons with a peak wavelength of 10µm (infrared). If the Earth’s average temperature is to remain constant, how many infrared photons must it emit for each green photon it absorbs?
*Q56.2) What’s the energy content of an ultraviolet photon with a wavelength of 200nm?
*Q56.3) What’s the frequency of an ultraviolet photon with a wavelength of 200nm?
**Q56.4) Wi-fi signals are typically carried by radio photons with a wavelength of 6cm. How many of these radio photons are required to have the same total energy content as a single photon of 400nm blue light?
**Q56.5) A typical chest x-ray imparts approximately 100 Joules of radiation energy to the patient. How many x-ray photons of wavelength 2nm would be absorbed by a patient during such an x-ray?