PhysBiochemWeekOne2011F - 1 Properties of Light Tue 3/28 2...

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1 1 1. Properties of Light 2. Absorption of Light by Molecules 3. Light reaction of Photosynthesis Tue 3/28 2 Iodine-131 is a gamma and beta emitter. All gamma rays emitted from a given isotope have the same energy. X-rays originate in the shell electrons, Gamma rays originate in the nucleus of a radioisotope. Light and Transitions • Light is considered to be a wave with an electric field component and a magnetic field component. • Linearly polarized bean of monochromatic light – light of one wavelength. • The monochromatic light repeats sinusoidally in time with the frequency , and in distance with wavelength 3 Light • A fundamental property of light is that it consists of oscillating electric and magnetic fields. • These fields carry the light’s energy and are responsible for the interaction of the light with material. • The two fields are always transverse ( perpendicular) to each other. • Here, the light ray is traveling to the right. • As the light travels, the electric field (E) oscillates along the vertical direction while the magnetic field (B) oscillates in and out of the page. • Also - light has both a particle nature and a wave nature. 4 Light m • Electric and magnetic fields oscillate. Electric and magnetic components are in phase. • together but perpendicular to each other. 6 Electric Field Magnetic Field Propagation of an Electromagnetic Wave through Space c
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2 Wavelength of Light 7 Wave properties • A wave can be characterized by its wavelength, but can also characterize it by the frequency (how many wavelengths pass a fixed point in a given time. Frequency is cycles per second (sec -1 ) or Hz. • Frequency is inversely proportional to wavelength • Sit on the dock of the bay---count the number of water waves passing in one minute. Frequency is the energy that the wave carries (think of a water wave knocking you over in heavy surf). Frequency, = c/ where c is the speed of light 8 Energy of a photon • Einstein determined that the energy of a photon is proportional to its frequency. • The higher the frequency, the greater the energy. • More generally, the theory states that everything has both a particle nature and a wave nature. • Atoms and molecules also exhibit wave motion. Each contain various energy states: vibrational, translational, and rotational energies. 9 Terms 10 Wavelength ( ) = distance between peaks. Frequency is the number of occurrences of a repeating event per unit time. Greek letter ( nu ). Frequency ( ) = waves/sec or cycles/sec, the number of wave crests passing a point per unit time. Speed of light (c) = 3 x 10 10 cm . s -1 = 186,000 miles s -1 Wavenumber is defined as the reciprocal of the wavelength. UNIT is reciprocal meters (inverse length). Wavenumber (tilde over nu) =
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This note was uploaded on 04/27/2011 for the course PHYS 2202 taught by Professor Mackie during the Spring '11 term at Temple.

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PhysBiochemWeekOne2011F - 1 Properties of Light Tue 3/28 2...

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