Determining the Focal Length of a Lens
Purpose
1. To observe the formation of an image by a converging lens and to determine the focal length (f) of a
converging lens using the mirror equation.
2. Test whether the magnification and mirror equation apply to a converging lens.
Variables
Manipulated:
object to lens distance (do)
Responding:
image to lens distance (di)
Controlled:
lens focal length (f)
Hypothesis
1
1
1
1
The variables will obey the mirror equation𝑑𝑖 + 𝑑𝑜 = 𝑓. If this equation is correct, then a graph of 𝑑𝑖 vs
1
𝑑𝑜
should have a slope of _____ (relate this to a physics equation) and an intercept of _____ (relate this
to y = mx + b).
Show work below
Apparatus
Procedure
Write procedure below
Data and Observations
do (cm)
di (cm)
1/do (cm-1)
1/di (cm-1)
Data Analysis
Using the y-intercept found from graphical analysis, determine the focal length of the lens. In
your response, provide a graph of the reciprocal of the image distance as a function of the
reciprocal of the object distance, determine the y-intercept of the graph, and relate the yintercept algebraically to a physics equation.
Using the slope of the graph found from graphical analysis, determine the magnification of the
image. In your response, determine the slope of the graph and relate the slope algebraically to
a physics equation. State all necessary physics concepts and formulas.