.ill AT&T; 5:17 PM 3396 (I + ?session.masteringphysics.cor ¢ e Ch22 Problems Pro

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.ill AT&T; 5:17 PM 3396 (I + ?session.masteringphysics.cor ¢ e Ch22 Problems Problem 22.5 17 of20 Constants You measure the focal length of a concave lens by first forming a real image of a light source using a convex lens. The image is formed on a screen 22 em from the lens. You then place the concave lens halfway between the convex lens and the screen. To obtain a sharp image, you need to move the screen 15 cm further away from the lenses. -Part A What is the focal length of the concave lens? Express your answer to two significant figures and include the appropriate units. Value Previous Answers Request Answer Incomect: Try Again;5 attermpts remaining Provide Feedback

Explanation / Answer

the image formed by conve lens is the virtual object for concave lens

for concave lens

object distance s = -22/2 = -11 cm

image distance s' = 11 + 15 = 26 cm

from lens equation

1/f = 1/s + 1/s'

1/f = -1/11 + 1/26

focal length f = -19 cm <<<----------ANSWER

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