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36.4 Thin Lenses Lenses are commonly used to form images by refraction in optical instruments, such the image S E C T I O N 3 6 . 4 • Thin Lenses 1141 3.0 cm 2.0 cm q n 2 n 1 n 1 > n 2 Figure 36.21 (Example 36.7) Light rays from a coin embedded in a plastic sphere form a virtual image between the surface of the object and the sphere surface. Because the object is inside the sphere, the front of the refracting surface is the interior of the sphere. from Table 36.2 that R is negative, we obtain The negative sign for q indicates that the image is in front of $ 1.7 cm q "
1.50 2.0 cm & 1 q " 1.00 $ 1.50 $ 3.0 cm
n 1 p & n 2 q " n 2 $ n 1 R
Example 36.8 The One That Got Away The apparent height h! of the fish is and the fish appears to be approximately three-fourths its " 0.752h h! " q
top $ q
bottom " $ 0.752d $ [$0.752(d & h)] A small fish is swimming at a depth d below the surface of a Solution Because the refracting surface is flat, R is infinite. Because q is negative, the image is virtual, as indicated by What If? What if you look more carefully at the fish and measure its apparent height, from its upper fin to its lower Answer Because all points on the fish appear to be frac- q
bottom " $ 0.752(d & h) q
top " $ 0.752d $ 0.752d q " $ n 2 n 1 p " $ 1.00 d " d q n 2 = 1.00 n 1 = 1.33 Figure 36.22 (Example 36.8) The apparent depth q of the fish is less than the true depth d. All rays are assumed to be paraxial. |