# Bb how does the object distance compare to the focal

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Unformatted text preview: ent. The focal length of the lens is 10mm. At what distance from the lens must the document be placed in order to obtain an image magnified by a factor of 5 that is NOT inverted? BB How does the object distance compare to the focal length? (A) s< f Lens Lens equation equation (B) s= f s> f (C) 111 =− s′ f s s′ = fs s− f Virtual Image ﬂ s’ < 0 Real object ﬂ s > 0 Converging lens ﬂ f > 0 h’ s’ h s f s− f <0 Physics 212 Lecture 26, Slide 24 24 A magnifying glass is used to read the fine print on a document. The focal length of the lens is 10mm. At what distance from the lens must the document be placed in order to obtain an image magnified by a factor of 5 that is NOT inverted? s′ = fs s− f BB What is the magnification M in terms of s and f? (A) M = Lens Lens equation: equation: 111 =− s′ f s fs ′= s s− f s− f f (B) M = f −s f (C) M = −f s− f (D) M = f s− f Magnification Magnification equation: equation: s′ M =− s h’ M= −f s− f s’ h s f Physics 212 Lecture 26, Slide 25 25 A magnifying glass is used to read the fine print on a document. The focal length of the lens is 10mm. At what distance from the lens must the document be placed in order to obtain an image magnified by a factor of 5 that is NOT inverted? M= −f s− f BB (A) 1.7mm (B) 6mm (C) 8mm (D) 40 mm (E) 60 mm M = +5 f = +10 mm M= −f s− f s= ( M −1) s= f M h’ 4 f = 8 mm 5 h s′ = − sM = −40 mm f Physics 212 Lecture 26, Slide 26 26 Follow Up Suppose we replace the converging lens with a diverging lens with focal length of 10mm. If we still want to get an image magnified by a factor of 5 that is NOT inverted, how does the object sdiv compare to the original object distance sconv? (A) sdiv < sconv (B) sdiv = sconv (C) sdiv > sconv (C) EQUATIONS M= −f s− f (D) sdiv doesn’t exist (D) PICTURES s= f M −1 M BB h h’ M = +5 f = −10 mm 4 s = f = −8 mm 5 s negative ﬂ not real object s f s’ Draw the rays: s’ will always be smaller than s Magnification will always be less than 1 Physics 212 Lecture 26, Slide 27 27 Follow Up Suppose we replace the converging lens with a diverging lens with focal length of 10mm. M= What is the magnification if we place the object at s = 8mm? (A) M = 1 2 (B) M = 5 EQUATIONS EQUATIONS M= −f s− f s = 8 mm f = −10 mm (C) (C) M= 3 8 (D) M= 5 9 (E) −f s− f M= 4 5 PICTURES −10 10 5 M =− = = 8 − (−10) 18 9 h BB h’ f Physics 212 Lecture 26, Slide 28 28...
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