We want to set up an experiment to measure the focal length of an unknown convex

Question

We want to set up an experiment to measure the focal length of an unknown convex lent Figure 1 show, the step for this experiment; it similar to what you did for your lent lab. but not the tame. The difference here it that the light source and convex lent are now anchored to the pole and are not allowed to move Instead, we will be moving the entire pole up and down to find the most focused image on the floor. Recall that we measured the length of the arrow on the light source to be 4.5 cm. The fixed distance from the arrow to the lens is 15 cm. Show your work in the spaces provided. We would generally be allowed to manipulate the image distance d_1 the object distance d and the total length L (i. e the distance from the object to the image). Which of these variables would be fixed and which would be varied in this experiment? After focusing the lens, we measure the length of the arrow on the floor to be about 27 cm long What is the magnification in this case? Can you find the image distance d, for this experiment? If so. find it. If not, write NO in the box and explain what additional information you would need. Can you find the focal length f of the lens? If so, find it and show your work. If not. put NO in the box and explain what additional information you would need. Is this setup a better way to measure the focal length vs, what was actually done in lab? Briefly discuss the errors and uncertainties in both setups. Grader: There is work on the back of this page.

Explanation / Answer

A. in the given experiment, object distance, do is fixed
image distance, di is variable
total length, L is variable
B. image height, Hi = 27 cm
object height, Ho = 4.5 cm
magnification, m = -Hi/Ho = -6
C. given do = -15 cm
di = ?
f = ? ( focal length)
but m = v/u = -6 = di/do
di = -6*do = 90 cm
D. using
1/di - 1/do = 1/f
1/90 + 1/15 = 1/f = 7/90
f = 90/7 cm = 12.857 cm

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