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UT Arlington ASTR 1345 - Exam 2 Study Guide

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ASTR 1345 1st EditionExam # 2 Study Guide Lectures: 11 - 17Lecture 11 (October 7)Electromagnetic WavesWhat are electromagnetic waves?Electromagnetic waves are electric and magnetic waves that are perpendicular to each other. They are measured by the speed of light (300,000 k/s).What is the electromagnetic spectrum?A spectrum is the result of electromagnetic radiation passing through a prism or grating so that different wavelengths are separated. The electromagnetic spectrum goes from the longest wavelength and lowest frequency: radio waves, microwaves, infrared radiation, visible light, ultraviolet radiation, X-Rays, and end in the shortest wavelength highest frequency which is gamma rays. Visible Light has a narrow range of wavelengths from 400nm to 700nm.What are the wave quantities?Speed is presented with a V and can also be represented as a C for EM waves and it is a constant, the speed of light. Wavelength is the distance between two successive peaks in a wave and is measured in nanometers (nm). Frequency is measured in Hertz and it’s the number of peaks or troughs of a wave that pass a fixed point each second. It’s the number of complete vibrations or oscillations per second. V= frequency X wavelength. If frequency increases then wavelength decreases and vice versa.What are the properties of light?Reflection, refraction, dispersion.Define reflection.Reflection is the rebounding of light rays off a smooth surface.Define refraction.Refraction: bending of light rays when they pass from one transparent medium to another.Define dispersion.Dispersion is the separation of light into colors.What are photons?Photons are a discrete unit of electromagnetic theory. Photon energy equals Planck ’s constant X the Speed of Light divided by wavelength. E=hf which is the energy of a wave= Planck ’s constant X frequency.How do color and frequency correlate?The color of light depends on frequency. Violet has the highest frequency at 400nm and the lowest wavelength. Red has the lowest frequency at 700 nm and the highest wavelength. We can see white when it absorbs all the colors and they’re all reflected back when we see black it’sthe opposite, none of the colors are reflected back. Lecture 12 (October 9)Properties of LightWhat are some more properties of light?Polarization, diffraction, and interference.Define Polarization.Polarization is the restriction of vibration of (transverse) wave to a particular direction.Define Diffraction.Diffraction is the bending of a light or wave behind an aperture or around an obstacle.Define Diffraction Grating.Diffraction grating consists of thousands of equally spaced fine lines ruled on a small rectangularplastic slide, used to give sharp interference maxima.Define Interference.Interference is the combo of two or more waves of the same type and wavelength which meet at a point in space.Define Constructive Interference.Constructive interference occurs when 2 waves are in phase, so the crests coincide.Define Destructive Interference.Destructive interference occurs when 2 waves are 90 degrees out of phase, so the crest of 1 wave coincides with the trough of the other.Why is the sky blue?The Sky is blue because sunlight contains all colors of the rainbow. Molecules of Earth’s atmosphere scatter incoming molecules in all directions. Blue (short wavelength) end of spectrum is scattered more than red (long wavelength) end.Why does the Sun appear orange or red?At sunrise or sunset the sun’s rays take a longer path through the atmosphere so more sunlight is scattered making the sun appear orange or red.What waves get to Earth’s atmosphere?Only visible light and radio waves reach the ground at all their wavelengths, while all infrared rays reach high mountains. Some UV rays get through, but most is blocked by the ozone layer. No X Rays or Gamma Rays get through because of Earth’s atmosphere.Lecture 13 (October 16)TelescopesWhat is the focal point?The focal point is the place at the focal length where light rays from a point object (one that’s too distant or tiny to resolve) are converged by a lens or concave mirror.What is the focal length?Focal Length is the distance from a lens or concave mirror to where converging light rays meet.What is the focal plane?Focal Plane is the plane at focal length of a lens or concave mirror on which an extended object is focused.What is the eyepiece lens?Eyepiece lens—magnifying lens used to view image produced at focus of telescope.What is magnification?Magnification is the number of times larger in angular diameter an object appears through a telescope than when it is seen by the naked eye.What are convex lenses?Convex lenses are lenses that’re thicker at their centers than at the edges. They cause the light that enters them to converge.What are concave lenses?Concave lenses are thinner at centers than around edges, cause light rays to diverge.What are objective lenses?Objective lenses are the principle lens in a refracting telescope (large convex lens). Large objective lenses use parabolic mirrors because 1. Neither spherical aberration nor chromatic aberration occur 2. They weigh less than large glass lenses 3. Unlike glass lenses, metal mirrors are structurally stable.Define refracting telescope.A refracting telescope or refractor is a telescope in which the principal light-gathering component is a lens.Why is spherical aberration a problem? What is a solution?A problem with a refracting telescope could be spherical aberration. This is an optical property where different proportions of a spherical lens or spherical concave mirror have slightly different focal lengths, producing a fuzzy image. A solution is making the lens very thin with a long focal length.What is chromatic aberration? What is a solution?Another problem could be chromatic aberration which is an optical property where different colors of light passing through a lens are focused at different distances from it. A solution is combining 2 lenses made from 2 different types of glass.Define reflecting telescope.A reflecting telescope or reflector is a telescope in which the principle light-gathering component is a concave mirror or spherical mirror.What is a problem and solution with this telescope?A problem with the reflecting mirror is that different parts of the mirror focus the light at different distances from the mirror. Solution to this is grinding the mirror to a parabolic shape.Define twinkling.Twinkling is the change in a


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