Lecture-6(1) - What did we learn in lecture # 5? 1/30/07 EM...

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1/30/07 Physics 20 Lecture 7 1 EM Waves EM Spectrum Black Body Radiation Emission Line Spectrum Absorption Line Spectrum Doppler Effect What did we learn in lecture # 5?
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1/30/07 Physics 20 Lecture 7 2 Lecture # 6: Telescopes How our eyes work? How lenses affect the light? Different types of telescopes Main characteristics of a telescope Why observing from space Adaptive optics technique Different observatories from ground and space Interferometry
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1/30/07 Physics 20 Lecture 7 3 Refraction of Light Focusing property of convex (converging) lenses is due to Index of Refraction (Snell’s Law) Lens has focal length Real-Inverted Image formed
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1/30/07 Physics 20 Lecture 7 4 The Eye • Light refracts into the eye through the cornea and then is further redirected by the lens. The shape of the eye lens is controlled by muscles, thus the eye has the ability to focus images on the retina. • Sometimes the cornea and eye lens are treated as a single “effective” thin lens. • For distant objects the focal length of the “relaxed” eye is about 2.50 cm. • When the eye is “fully accommodated” objects as near as 25 cm can be focused. This is called the near point. • Myopia (nearsightedness) occurs when the lens is too strong or the eye too long. • Hyperopia (farsightedness) occurs when the lens is too weak or the eye too short. • LASIK (Laser in situ Keratomileusis) reshapes cornea by laser ablation.
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1/30/07 Physics 20 Lecture 7 5 Simple Magnifying Glass Use converging magnifying lens to create image at “near point” which is enlarged Magnification M 25 cm f
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1/30/07 Physics 20 Lecture 7 6 Galilean Telescope p 1 → ∞ q 1 = f obj p 2 = f eye q 2 → −∞ M = f obj Λ Ν Ξ Π −∞ f eye Λ Ν Μ Ξ Π Ο = f obj f eye For f obj = 100 cm and f eye = 2.5 cm M = 40
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1/30/07 Physics 20 Lecture 7 7 Main Properties of Telescopes Light collecting area: tells us how much light the telescope could collect at any given time. This is normally characterized by defining the diameter of a telescope Angular Resolution: is the smallest angle over which one can separate two dots (or two stars). Our eyes have an angular separation of 1 arcmin which means we could distinguish two stars if they are separated by > 1 arcmin.
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Lecture-6(1) - What did we learn in lecture # 5? 1/30/07 EM...

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