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Chapter Three Notes: Radiation

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Brian Wilson

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Radiation: Information from the Cosmos 3.1 Information from the skies - The Andromeda galaxy is comparable in diameter to the full moon - lies roughly 2.5 million light years away - even if a space probe could travel at the speed of light, it would need 2.5 million years to reach this galaxy and 2.5 million more to return Since it is practically impossible to travel such far distances in the universe, how do astronomers know anything about objects far from earth? We use the laws of physics as we know them here on earth to interpret the electromagnetic radiation emitted by those objects Light and radiation - Radiation: any way in which energy transmitted through space from one point to another without the need for any physical connection bw the two locations. - The term electromagnetic just means that the energy carried is in the form of rapidly fluctuating electric and magnetic fields. - Electromagnetic theory provides us with answers to questions regarding masses, temperature and proportion of galaxies and planets in the universe. - Visible lightis the particular type of electromagnetic radiation to which our human eyes happen to be sensitive. - Modern instruments can detect many forms of invisible electromagnetic radiation which goes completely unnoticed by our eyes such as radio, infrared and ultraviolet waves, also x rays and gamma rays www.notesolution.com- Despite the different names, the words light, rays, radiation and waves all really refer to the same thing. - The names are just historical accidents because it took many years for scientists to realize that all these forms of radiation are in reality one and the same physical phenomenon. Wave Motion - All electromagnetic radiation travel through space in the form of waves - A wave is a way in which energy is transferred from place to place without the physical movement of material from one location to another. - In wave motion the energy is carried by a disturbance of some sort - This disturbance, wtv its nature, occurs in a distinctive repeating pattern - Similar to sound waves in the air, or ripples on the surface of a pond - A wave is not a physical object - An example of a disturbance is throwing a pebble into a lake; the ripples then might cause a nearby twig to float somewhere else. - (refer to figure 3.3 on pg 59) ; shows how wave properties are quantified and illustrates terminology - The waves period is the number of seconds needed for the wave to repeat itself at any given point in space - The wavelength is the number of meters needed for the wave to repeat itself at a given moment in time - It can be measured as the distance between two adjacent wave crests, two adjacent wave troughs, or any two similar points on adjacent wave cycles. - A wave moves a distance equal to 1 wavelength in one period - The max departure of the wave from the undisturbed state is called the waves amplitude. (eg. Flat pond surface) - The number of wave crests passing any given point per unit time is called the waves frequency www.notesolution.com
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