Chapter 25, Problem 21 Refer to Interactive Solution 25.21 for help with problem

Question

Chapter 25, Problem 21 Refer to Interactive Solution 25.21 for help with problems like this one. A concave mirror (R - 83.8 cm) is used to project a transparent slide onto a wall. The slide is located at a distance of 49.2 cm from the mirror, and a small flashlight shines light through the slide and onto the mirror. (a) How far from the wall should the mirror be located? (b) The height of the object on the slide is 1.45 cm. What is the height of the image? Units (a) Number (b) Number Click if you would like to Show Work for this question: Units Open Show Work

Explanation / Answer

Using the equation 1/u + 1/v = 1/f .. [no sign changes as image is real, f = ½ R]

(a) Image distance = v
1/v = 1/f -1/u = 1/41.9cm - 1/49.2cm = 0.00354 ..
v = 1/ 0.00354 .. .. v = 282.4 cm

(b) Magnification = v/u = 282.4/49.2 = 5.74
Image height = 5.74 x 1.45cm .. .. h = 8.32 [the - sign is added to indicate an inverted image]

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