Question

Two lenses of +15D and -15D are in contact with each other forming a combination lens. (i)What is the focal length of this combination?(ii)An object of size 3 cm is placed at 30cm from this combination of lens. Calculate the position and size of the image formed.

Answer 1

Explanation:

Given Two lenses of +15D and -5D are in contact with each other forming a combination lens. (i)What is the focal length of this combination?(ii)An object  of size 3 cm is placed at 30cm from this combination of lens. Calculate the position and size of the image formed.

• Power of combination P = P1 + P2  
•                                            = 15 D + (- 5 D)
•                                            = 10 D
• Now focal length will be F = 1/P
•                                              = 1/10
•                                               = 0.1 m
•                                            = 10 cm
• Now we have 1/f = - 1/u + 1/v
•                         1/10 = -1/-30 + 1/v
•                     1/v = 1/10 - 1/30
•                        v = 15 cm
• now magnification m = f / u + f
•                                      = 10 / - 30 + 10
•                                      = - 1/2  
• Therefore size of the image = 3 x (- 1/2 )
•                                                    = - 3/2
•                                                    = - 1.5 cm
• So image is inverted.

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https://brainly.in/question/7886994