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Use this simulation to explore how light interacts with molecules in our atmosphere.

Explore how light interacts with molecules in our atmosphere.

Identify that absorption of light depends on the molecule and the type of light.

Relate the energy of the light to the resulting motion.

Identify that energy increases from microwave to ultraviolet.

Predict the motion of a molecule based on the type of light it absorbs.

Check Your Understanding How do the electromagnetic waves for the different kinds of electromagnetic radiation differ?

They fall into different ranges of wavelength, and therefore also different corresponding ranges of frequency.

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Summary

  • The relationship among the speed of propagation, wavelength, and frequency for any wave is given by v = f λ , so that for electromagnetic waves, c = f λ , where f is the frequency, λ is the wavelength, and c is the speed of light.
  • The electromagnetic spectrum is separated into many categories and subcategories, based on the frequency and wavelength, source, and uses of the electromagnetic waves.

Key equations

Displacement current I d = ε 0 d Φ E d t
Gauss’s law E · d A = Q in ε 0
Gauss’s law for magnetism B · d A = 0
Faraday’s law E · d s = d Φ m d t
Ampère-Maxwell law B · d s = μ 0 I + ε 0 μ 0 d Φ E d t
Wave equation for plane EM wave 2 E y x 2 = ε 0 μ 0 2 E y t 2
Speed of EM waves c = 1 ε 0 μ 0
Ratio of E field to B field in electromagnetic wave c = E B
Energy flux (Poynting) vector S = 1 μ 0 E × B
Average intensity of an electromagnetic wave I = S avg = c ε 0 E 0 2 2 = c B 0 2 2 μ 0 = E 0 B 0 2 μ 0
Radiation pressure p = { I / c Perfect absorber 2 I / c Perfect reflector

Conceptual questions

Compare the speed, wavelength, and frequency of radio waves and X-rays traveling in a vacuum.

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Accelerating electric charge emits electromagnetic radiation. How does this apply in each case: (a) radio waves, (b) infrared radiation.

a. Radio waves are generally produced by alternating current in a wire or an oscillating electric field between two plates; b. Infrared radiation is commonly produced by heated bodies whose atoms and the charges in them vibrate at about the right frequency.

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Compare and contrast the meaning of the prefix “micro” in the names of SI units in the term microwaves .

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Part of the light passing through the air is scattered in all directions by the molecules comprising the atmosphere. The wavelengths of visible light are larger than molecular sizes, and the scattering is strongest for wavelengths of light closest to sizes of molecules.
(a) Which of the main colors of light is scattered the most? (b) Explain why this would give the sky its familiar background color at midday.

a. blue; b. Light of longer wavelengths than blue passes through the air with less scattering, whereas more of the blue light is scattered in different directions in the sky to give it is blue color.

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When a bowl of soup is removed from a microwave oven, the soup is found to be steaming hot, whereas the bowl is only warm to the touch. Discuss the temperature changes that have occurred in terms of energy transfer.

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Certain orientations of a broadcast television antenna give better reception than others for a particular station. Explain.

A typical antenna has a stronger response when the wires forming it are orientated parallel to the electric field of the radio wave.

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Source:  OpenStax, University physics volume 2. OpenStax CNX. Oct 06, 2016 Download for free at http://cnx.org/content/col12074/1.3
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