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**Unformatted text preview: **Class 20 Optical Devices, Review 2 Physics 106 Fall 2011 Press CTRL-L to view as a slide show. Last Time Last time we discussed: I The Eye I Single Slit Diffraction I Polarization I Thin Film Examples Learning Outcomes Today’s topics are: I Optical systems I Test Review Optical Systems Angular Magnification I Angular magnification is defined as m = θ θ = angle with lens angle without lens Angular Magnification I For a simple magnifying lens: m = 25cm f Compound Microscope I The objective lens makes a real image I The eyepiece is a magnifier to view details of the real image Compound Microscope I The objective lens has a short focal length, f o < 1 cm I The eyepiece has a focal length f e of a few cm Magnifications of the Compound Microscope I The lateral magnification of the objective lens is usually marked on it, e.g., × 30 I The angular magnification of the eyepiece is also marked on it, e.g., × 10 I The overall magnification of the microscope is the product of the individual magnifications, here: times 300 Telescopes Two fundamental types of telescopes: I Refracting telescope: has an objective lens I Reflecting telescope: has an objective mirror Refracting Telescope I An objective lens forms a small real image I An eyepiece is a magnifying glass to view the real image I The focal point of the eyepiece is placed near the first image I The length of tube is f o + f e I The eyepiece forms an enlarged, inverted, virtual image of the first image Angular Magnification of a Telescope I The angular magnification depends on the focal lengths of the objective and eyepiece m = θ θ = f o f e Reflecting Telescope, Newtonian Focus I Incoming rays reflect and converge toward point A I A small flat mirror, M, reflects the light to the eyepiece The Test The Test I 25 multiple choice questions I Chapters 20-24 I Excluding Single Slits and Polarization I Look at the chapter reviews I Look over quizzes I Review these slides Chapter 20 Key Idea Faraday’s Law I When the number of magnetic field lines through a coil of wire changes, an induced current flows through the loop I Or . .. Changing magnetic fields produce electric fields that form loops. Key Idea Lenz’ Law I Induced current flows in the direction that opposes change in flux. Equations I Flux Φ B = BA cos θ I Faradays’ Law =- N ΔΦ B Δ t Problem 1 The north pole of a magnet is moving away from a loop of wire. Which way does the current flow? A. Definitely CW B. Probably CW C. Definitely CCW D. Probably CCW E. Don’t know Problem 2 The magnetic field through a loop of radius 2.00 cm is increasing at the rate of 0.30 T/s. What is the EMF around the loop? A. 0.3 V B. 0.3 × π × . 02 2 V C. 2 × π × . 3 2 V D. Don’t know Problem 2a If there is a 3 Ω resistor in the circuit, what current flows? Key Idea and Equation Motional EMF I If a wire of length L moves perpendicularly to a magnetic field, the electric and magnetic forces balance: qE = qvB , E = / L I = BLv Problem 3 A wire 3.0 cm long moves through a 0.20 T magnetic field at aA wire 3....

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