Asked by Lena

I was asked to compare my measured focal length to my calculated focal length. My calculated focal length I figured out by using the formula:

1/di + 1/do = 1/f

Would my measured focal length = my di?
I only measured by di and do in the actual experiment.
Answered by Lena
The experimental values I have are:
f=12
object location = 2.5f
object distance from lens = 35 cm
image distance from lens = 27 cm
Answered by drwls
The "measured focal length" is the value of f that you compute using the lens formula and your measured values of di and do. In this case, that would be given by
1/27 + 1/35 = 1/f,
which leads to f = 15.2 cm

According to your measurements, the focal length is not 12 cm.

If you were supposed to have an object location of 2.5 f and the focal length were really 12 cm, the object should have been placed 30 cm from the lens, not 35.

How did you get the "experimental value" of f = 12 cm? Did they tell you what it is?
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