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Pitt ASTRON 0087 - Exam 3 Study Guide
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ASTRON 0087 1st EditionExam #3 Study Guide Chapters: 9-12Chapter 9: Light-the Cosmic MessengerDoes light need a medium to be transferred?Nope.How does light act? As a wave, or as a particle?It acts as both! It acts as a wave in that it has varying electrical and magnetic fields (it’s also called electromagnetic radiation). However, an individual particle of light is called a photon.What’s a photon?It’s a particle of light. It doesn’t have mass or a charge, but it has energy.What are the three ways that you can characterize light?You can characterize light in three ways. The first is by its wavelength, which is the space between crests in the wave. It’s measured in nanometers. The second is by its frequency, or the number of crests in the wave that pass a viewer in the time frame of a second. It’s measured in Hz, or cycles per second (crests per second). The third is the level of energy that a photon in the light has. What’s the speed of light?All light travels at a speed of 300,000 km/second.Talk about Visible Radiation:Visible radiation is essentially the light that we are able to see. It starts with red light, which has the longest wavelength and the lowest frequency, and goes all the way up to violet, which has a short wavelength and a high frequency.Spectrum of light:Gamma rays -----------------------highest frequency, highest energy, shortest wavelengthX-RaysUltraviolet LightVisible LightInfraredRadio ----------------------------------- lowest frequency, lowest energy, largest wavelengthHow does light interact?Four ways: (1) it can be emitted, such as by the sun or a tungsten filament, (2) it can be absorbed, such as by a dark shirt, (3) it can be transmitted, or moved through, such as how light goes through a window, and (4) it can be reflected, such as when light hits a mirror.What are the different types of spectra?1. Continuous Spectrum: the intensity changes smoothly with the wavelength (or color) – a source that produces a continuous spectrum of light is a lightbulb.2. Emission Line Spectrum: when light is emitted at only a few different wavelengths – source that produces this is a hot, tenuous gasa. Lines will only show up on a spectrometer if the intensity is more than the intensity of the light around it.3. Absorption Spectrum: A continuous band of light on which dark lines are seen. Dark lines appearwhen the intensity of the light at that point is less than the intensity of the light around it. This type of spectrum shows up when you look at a something producing a continuous spectrum of light through a cooler gas.What are atoms?Atoms are the fundamental building blocks of matter. They are made out of protons, electrons, and neutrons. All of the neutrons (neutral charge) and protons (positive charge) are found in the nucleus, while the electrons (negatively charged particles) orbit them. There are equal numbers of electrons and protons and there are usually about as many neutrons as protons. Electrons must orbit in a specific number (not just any orbit is allowed). Every atom, molecule, and ion has its own specific charge. What creates a spectral line?A spectral line is created when the number of electrons changes in an atom, ion, or molecule. This change can either be an emission of an electron (when an electron is let go, resulting in more energy in anarrow band) or an absorption of an electron (resulting in less energy in a narrow band). Emission lines are created when an electron is emitted and show up in color on a black background. Absorption lines are created when an electron is absorbed and show up as black lines on a continuous background. Atoms, Ion, and Molecules each have their own unique spectral signature. (this is important)Why bother studying a spectrum?It can show us the composition of stars, or the composition of the atmosphere. It can also reveal the temperature of the spectrum, the pressure of any gases in the spectrum, and how anything is moving.What’s a neutral atom?An atom that has no charge (it has the exact same number of neutrons and protons).When is an atom or ion in ground state?When all electrons are in their lowest energy state.What’s the excited state?An atom that is in an excited state is experiencing the addition of energy that causes their electrons to occupy a higher energy level. What does the term ionized mean?An atom is ionized when enough energy is added to it so that one or more of its electrons gets enough energy to escape completely. The atom now has a charge because there isn’t the same number of protons and electrons. Atoms are ionized when they bump into each other or absorb a lot of radiation, such as from the sun.What’s the Doppler Effect?The Doppler Effect is the change in wavelength of when the source of the waves and the person observing the waves are moving in relation to each other. When waves are coming towards you, it seemslike they have a decreasing wavelength. When waves are moving away from you, their wavelength seemsto get longer. The change in wavelength can be used to measure the speed of the object that is emitting the waves. It lets us see that the stars are rotating.What are telescopes used for?THEY ARE USED TO GATHER LIGHT, NOT MAGNIFY VISION.How is the size of the lens and the ability to gather light related?Telescopes that have larger lenses will be able to collect more light.How do refracting telescopes work?Refracting telescopes work by using a lens to concentrate the light that’s coming in to a single point, called the focal point. How do reflecting telescopes work?Reflecting telescopes work by using a curved mirror to reflect the light back to the viewer to form an image.Which is better?Reflecting telescopes tend to be better because they are stronger and more durable. They can be made to be larger and less expensive. Basically all modern telescopes are reflectors because they are more consistent (light traveling through a refracting telescope will refract different based on its wavelength), some of the light travelling through a refracting lens is absorbed, and that the biggest, best lenses are very heavy (which makes a refracting telescope unable to use them since the end can only be supported on its edges). Using a lens rather than a mirror for a telescope requires two surfaces and will also cause chromatic aberration (the colors won’t be the same). How does the amount of light collected relate to the radius of the mirror?The amount of light collected


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Pitt ASTRON 0087 - Exam 3 Study Guide

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