Lec26-1V - Lecture 26-1 Lecture Lens Equation(<0 111 = pqf...

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Lecture 26 Lecture 26 -1 Lens Equation 11 1 pq f + = ( < 0 ) ¾ True for thin lens and paraxial rays . ¾ magnification m = h’/h = - q/p
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Lecture 26 Lecture 26 -2 Signs in the Lens Equation for Thin Lenses 11 1 pq f + = q m p = − p is positive for real object q is positive for real image q is negative for virtual image m is positive if image is upright m is negative if image is inverted f is positive if converging lens f is negative if diverging lens i o yf qq p == p is negative for virtual object
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Lecture 26 Lecture 26 -3 Geometric Optics vs Wave Optics Geometric optics is a limit of the general optics where wave effects such as interference and diffraction are negligible. ¾ Geometric optics applies when objects and apertures involved are much larger than the wavelength of light. ¾ In geometric optics, the propagation of light can be analyzed using rays alone. Wave optics (sometimes also called physical optics ) - wave effects play important roles. ¾ Wave optics applies when objects and apertures are comparable to or smaller than the wavelength of light. ¾ In wave optics, we must use the concepts relevant to waves such as phases, coherence, and interference .
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Lecture 26 Lecture 26 -4 READING QUIZ 1 Which of the following statements is incorrect ? A| Wave optics applies when objects and apertures are comparable or smaller than the wavelength of light. B| Two light waves of different frequency f = c/ λ , where λ is the wavelength and c is the light velocity, exhibit interference fringes. C| When the difference in phase of two or more waves remains constant (time independent) the waves are perfectly coherent. D| A LASER is a source of a single frequency perfectly coherent light. E| An incandescent light emits light that has a short (~ 1 meter ) coherence length.
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Lecture 26 Lecture 26 -5 Coherence ¾ When the difference in phase between two (or more) waves remains constant (i.e., time-independent), the waves are said to be perfectly coherent . For a “single” wave: Only coherent waves can produce interference fringes! Coherence length : the longitudinal extent over which light waves remain coherent. ¾ A single light wave is said to be coherent if any two points along the propagation path maintains a constant phase difference . - laser light is coherent. light transmitted through a small aperture is more or less coherent. - light from a light bulb and sun light over some area are in coherent [along their length].
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Lecture 26 Lecture 26 -6 Interference of Two Coherent Waves Constructive interference ( in phase ) In both figures, red is the SUM Snapshot of wave fronts at a given instant Destructive interference ( exactly out of phase ) 2 0 2 12 () Ic E EE ε = ∝+ B,C A
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Lecture 26 Lecture 26 -7 Intensity of Interference Fringes Let the electric field components of two equal- strength coherent electromagnetic waves AT SOME POINT IN SPACE be 10 20 sin sin( ) EE t t φ ω = = + The resulting electric field component is then [] 12 0 0 sin sin( ) 2c o s s i n 22 E Et
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This note was uploaded on 04/23/2011 for the course PHYS 241 taught by Professor Wei during the Spring '08 term at Purdue.

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Lec26-1V - Lecture 26-1 Lecture Lens Equation(<0 111 = pqf...

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