PLEASE READ before answering. Last 2 people haven\'t and both were wrong answers

Question

PLEASE READ before answering. Last 2 people haven't and both were wrong answers.

The figure shows a combination of two identical lenses of focal length 9 cm. Part A Find the distance from the original object to the final image. Part B Find the height of the final image if the object is 2.0 cm in height. Part C Is the final image erect or inverted? Please show work and use f for focal point, i for image and o for object such as 1/f = 1/i + 1/o.

Solve this using that formula and proceeding to do it for 2nd lens. DONT try and combine into one formula. Not helpful and won't get credit. Im doing something wrong with my getting my i1 which I know is used for Object 2 (using O2=D (dist betw lenses - i1).

Explanation / Answer

ANSWER

Part a)

For first lens,

1/i + 1/o = 1/f
1/i + 1/36 = 1/9
1/i = 4/36 - 1/36 = 3/36 = 1/12
i = 12

This acts as the object for the second lens,

o = 15-12=3
1/i + 1/o = 1/f
1/i + 1/3 = 1/9
1/i = 1/9 -3/9 = -2/9
i= -4.5 cm

So distance from object,

36+15-4.5=46.5 cm

Part b)

M = m1 m2 = i1 i2/(o1 o2) =(12*-4.5)/(3*36)=-0.5
h' = 2*0.5 = 1 cm

Part c)

M is negative so inverted.

Regards!!!

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