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Unformatted text preview: Lecture 1 Notes B. A. Rowland 53750 I will outline a few highlights from the first lecture in these notes. These are written in conjunction with the slides presented in class. Light For years light was thought to be a wave. There are some terms you should be familiar with concerning waves: Wavelength : The distance between two successive crests (or troughs) in a wave. Units of distance (m, mm, cm, nm, etc). Frequency: The number of cycles per second that pass through a given point in space. Units of 1/s (also known as the HertzHz). Speed : The velocity of the traveling wave. In a vacuum, for EMR this value is c = 2.998 x 10 8 m/s. Wavelength and frequency are inversely proportional. This means that as the wavelength increases, the frequency decreases and vice versa. Important equation: c = , where is the wavelength and is the frequency. Make sure to watch your units! For any wave the wavelength times the frequency should equal the speed of light ( c ). The energy of light is directly proportional to the frequency, while it is inversely proportional to the wavelength. Practice Problem: Green light has a wavelength of 530 nm (nanometers). What is the frequency of green light? Red light is less energetic than violet light. This means that red light will have a _________ (higher, lower) wavelength and ____________ (higher, lower) frequency than violet light. EMR Light is a form of Electromagnetic Radiation and represents only a very small fraction of the Electromagnetic Spectrum. Other examples of EMR and their effects on matter include: Radio wavesexcites nuclei. Microwavesmakes molecules rotate. Infraredmakes molecules vibrate. Visible lightcauses electronic transitions in molecules which produce pretty colors. Ultravioletalso causes electronic transitions. X-rayremoves electrons from molecules. Gamma rayslikely would obliterate molecules. Each of these types of radiation does something a little different to a molecule, and we can use this information to make predictions as to the structure of molecules (field of spectroscopy). The concepts of wavelength and frequency can be applied to EMR, and all the principles discussed above apply as well....
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This note was uploaded on 02/02/2009 for the course CH 53750 taught by Professor Rowland during the Spring '09 term at University of Texas at Austin.
- Spring '09