SNC2D
Lab: Images Produced by Converging Lenses
Submission & Evaluation: Each student will submit a formal lab report. The formal lab report rubric for this lab is at the
end of this document.
The report should be clearly organized and include:
Purpose
Hypothesis
Materials
Procedure
Observation Table
Analysis
Discussion/Conclusion
Extension
Refer to the Nelson Skills Handbook posted on ANGEL, p.601, 611-617
Purpose: The purpose of this investigation is to determine the relationship between the focal length, the image distance
and the object distance of a converging lens.
In this lab you will be investigating 5 cases in which the resulting image will differ based upon the location of the object
with respect to the lens:
 Case 1: the object is located beyond 2f
 Case 2: the object is located at 2f
 Case 3: the object is located between 2f and the focal point (f)
 Case 4: the object is located at the focal point (f)
 Case 5: the object is located in front of the focal point (f)
Hypothesis: Make a statement in response to the purpose. It should clearly conjecture an outcome that covers every
case and is testable. It should address all the LOST characteristics.
It should be in the form “As the object moves closer to the lens, the image
__________________________________________________________________________________________________
________________________________________________________________________________.”
Materials:
 Record a detailed list of all materials you use in this lab. Be specific. For example, instead of saying “track” you could
say “1 m long track”.
Safety Considerations:
 Watch when moving equipment that you don’t tip the track off the desk or accidentally hit another student.
Remember Sign Conventions:
 Object and image distances are measured from the optical centre of the lens.
 Object distances are positive if they are on the same side of the lens from which the light is coming; otherwise they
are negative.
 Image distances are positive if they are on the opposite side of the lens from which the light is coming; if on the
same side, the image distance is negative. (Image distance is positive for real images and negative for virtual images)
 Object heights and image heights are positive when measured upward and negative when measured downward
from the principal axis
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SNC2D
Procedure:
 You must come up with the procedure for this lab and record it in your lab report. Remember, procedure steps
should be simple, present-tense, actions that another student could complete in order to get your same results. The
first couple have been completed for you below. You still need to include them in your lab report.
1. Determine the focal length of your converging lens. Set your ray box to send out a wide beam of light and hold it
about a metre away from your lens. Use your screen to locate the point on the opposite side of the lens where the
light is focused to a point.
Measure the distance between the screen and the lens:
f = ______
2. Turn the lens around and repeat step 1 (to verify your measurement)
f = ______
3. Calculate an average of both f measurements.
favg= ______
4. Using this average value, calculate the following object distances and record them in the attached table:
2.5f = ___ 2.0f = ___
1.5f = ___
f = ___
0.5f = ___
5. Start adding your own steps here.
Observations:
Complete the observation table below and perform relevant calculation. Remember sign conventions!
Case
Object
L
O
S
T
1/ do
1/ di
1/ do +
1/f
Distance
(di), cm
(hi),
1/ di
(do), cm
cm
1
2.5f = ___
2
2.0f = ___
3
1.5f = ___
4
f
5
0.5f = ___
= ___
Show sample calculations in your lab report.
Analysis:
1. As the object moves closer the lens what regular changes occur:

to the size of the image?

to the distance of the image?

to the attitude of the image?
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SNC2D
2. At what object distance was it difficult, if not impossible, to locate a clearly focused image?
3. Where would you place an object in relation to the principal focus to form a:
 real image?

virtual image?
4. How does the value of 1/f relate to the value of (1/ do + 1/ di ) for the cases involving real images?
5. How does the value of 1/f relate to the value of (1/ do + 1/ di ) for the cases involving virtual images?
6. Calculate the theoretical di for each case and find your percent error.
Discussion/Conclusion:
1. Why does the method in step 1 work for finding the focal length of the lens? (hint – check out the rules for rays in a
converging lens and draw a ray diagram to help you explain your reasoning)
2. The thin-lens equation is
1 1 1

 . Has your experiment confirmed or contradicted this relationship?
f d o di
3. Can you provide some suggestions on how to increase the accuracy of the experiment? (Consider parts that you
found difficult)
4. Based on your investigation and findings – what is the relationship among the focal length, the image distance and
the object distance of a converging lens?
Extension:
Match the following real-world device listed below to the characteristics you observed in your 5 object/image
orientations.
Object Distance
Image Location and
Device
(In terms of f )
Attitude
Photocopier
(Image is the same size, and real)
Hand Magnifier
(image is larger and virtual)
Overhead Projector
(image is larger and real)
35 mm Camera
(image is smaller and real)
Spotlight
(parallel light – there is no image)
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SNC2D
Category
Level 4
Level 3
Level 2
Level 1
Below Level 1
Knowledge
Understanding Concepts and
Terminology. Overall lab submission
demonstrates thorough and insightful
understanding of concepts related to
refraction.
No submission or
below Level 1
expectation.
Thinking
Hypothesis clearly conjectures the
relationship between variables that
covers every case listed in Purpose.
No submission or
below Level 1
expectation.
Procedure steps logical and
reasonable. They could be easily
followed by another person.
No submission or
below level 1
expectation.
Observation table is complete and
correct with sample calculations
shown.
No submission or
below level 1
expectation.
All 6 Analysis questions are complete
and correct, with thorough supporting
evidence.
No submission or
below level 1
expectation.
All 4 Discussion answers are
thorough, logical, complete and
correct.
No submission or
below Level 1
expectation.
Communication
All required elements are present and
additional elements that add to the
report (e.g., thoughtful comments,
graphics) have been added and the
report is on time.
No submission or
below Level 1
expectation.
Lab is well organized using the proper
format, relevant vocabulary,
mathematical conventions and units.
No submission or
below Level 1
expectation.
Application
Extends refraction of converging
lenses to real-life applications.
Complete and correct for all 5.
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No submission or
below Level 1
expectation.