S10P1CLec24A

# S10P1CLec24A - Physics 1C Lecture 24A "There are two kinds...

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Physics 1C Lecture 24A "There are two kinds of light--the glow that illuminates, and the glare that obscures." --James Thurber

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Two Lens System Example Two converging lenses with focal lengths of 40cm and 20cm are placed 10cm apart. A 2cm tall object is located 15cm from the 40cm focal length lens as shown in the Fgure. ±ully describe the resulting image. Answer The center of the Frst lens is our origin. Object f 1 =40cm f 2 =20cm 10cm 15cm 2cm
Thin Lens Equation Answer First, turn to the thin lens equation for the ±rst lens: where the negative sign means that the image is on the same side of the lens as the object (the left). The magni±cation of the object from the ±rst lens will be: 1 p + 1 q = 1 f 1 q = 1 f 1 1 p = 1 40cm 1 15cm 1 q = 3 120cm 8 120cm = 5 120cm q = 120cm 5 = 24cm M 1 = q p = 24cm 15cm = + 1.6

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Thin Lens Equation Answer Next, turn to the thin lens equation for the second lens. But now the object distance will be the distance from the image of the Frst lens to the second lens. Since the image is 24cm to the left of the Frst lens and the two lenses are 10cm apart, this means that object distance to the second lens is 34cm. The Fnal image is to the right of the second lens. 1 p + 1 q = 1 f 1 q = 1 f 2 1 p = 1 20cm 1 34cm 1 q = 17 340cm 10 340cm = 7 340cm q = 340cm 7 = 48.6cm
Thin Lens Equation Answer The magnifcation oF the object From the second lens will be: The total magnifcation oF the object through the two lens system will be: M 2 = q p = 48.6cm 34cm = 1.43 M Tot = M

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## This note was uploaded on 06/03/2010 for the course PHYS PHYS 1C taught by Professor F during the Spring '00 term at UCSD.

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S10P1CLec24A - Physics 1C Lecture 24A "There are two kinds...

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