In a variation of the lens experiment

PHYSICS · Multi-part · AP · Physics 2: Algebra-based · Geometric Optics · Geometric Optics

Problem

In a variation of the lens experiment, a student cannot directly measure the image distance

s_i

but instead measures the height of the sharp image formed on a screen. For each trial she records the object distance

s_o

, the object height

h_o=1.5\,\text{cm}

, and the image height

h_i

(negative values indicate inverted images).

Trial	$s_o$ (cm)	$h_i$ (cm)
1	25.0	−4.5
2	30.0	−3.0
3	35.0	−2.1

Real distances are taken as positive. The accepted focal length for this lens is

20.0\,\text{cm}

. (a) For each trial, determine the magnification

M

of the image. (b) Using the magnification from part (a), compute the corresponding image distance

s_i

for each trial. (c) Determine the focal length for each trial and then calculate the mean focal length. (d) Compute the percent difference between the mean focal length from part (c) and the accepted focal length. Based on this result, comment on the reliability of using magnification rather than direct measurement of

s_i

in this context.

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