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Pre-AP Physics Thin Lens Equation & Magnification. Allen High School. Thin Lens Equation. Ray Diagrams only give an estimate for image size and distance. The equation gives you more accurate values. f = focal length d o = object distance d i = image distance.
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Pre-AP PhysicsThin Lens Equation & Magnification Allen High School
Thin Lens Equation • Ray Diagrams only give an estimate for image size and distance. • The equation gives you more accurate values. • f= focal length • do = object distance • di = image distance
Can’t you just flip it all over? • Let’s see:
Example 1 • Sadie looks at her friend’s face through a converging lens. If her friend’s face is 50 cm from the lens that forms an image at a distance of 20 cm, what is the focal length of the lens?
Example 2 • Dr. Wasserman is showing slides to his biology class. If the slides are positioned 15.5 cm from the projector lens that has a focal length of 15 cm, where should the screen be placed to produce the clearest image of the slide?
Magnification • Previously, we described the magnification of an image qualitatively, now we have two equations that will quantify it. • M = 1 (image is same size as object) • M > 1 (image is bigger than object) • M < 1 (image is smaller than object) • M is positive means object & image are same orientation. • M is negative means object & image are opposite orientation.
Example 1 • If an object sitting 25 cm in front of the lens forms an image 20 cm behind the lens, determine the magnification.
Example 2 – Super Duper! • Marlin is out on a safari. Looking through the telescope, he spots a giraffe 5 m away. The telescope lens has a focal length of 2 m. A) How far away is the giraffe really standing? B) What is the magnification? C) If the giraffe is really 8m high, what is the apparent height of the giraffe through the lens?