Investigating Converging Lenses - Guided
PSI Physics – Geometric Optics
Name______________________
Date__________ Period_______
Description and Objectives
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To measure the focal length of a converging lens
To find the characteristics of images produced by converging lens
To find optical properties of converging lens
A convex or converging lens is thicker in the middle of the lens and converges at
the edge of the lens. The principal axis of the lens is an imaginary perpendicular to the
geometric center of the lens. At some distance from the lens on the principal axis is
the focal point (f) of the lens. Light rays that strike the lens parallel with the principal
axis converge at this point. The exact location of the focal point of the lens depends on
both the shape of the lens and the index of refraction of the material making up the lens.
Twice the focal length from the lens is an important position called 2f. If the lens
is symmetrical, the focal point f and point 2f are located the same distance to the left of
the lens as the corresponding points are located to the right. During this investigation
you will observe optical properties of convex lenses.
Materials
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Double Convex (Converging) Lens
Meter stick
Screen
Light Source (light bulb, PASCO Basic Optics Light Source)
Optics Ramp
Holders (lens, screen, light source)
Procedure
1. Place on the optics ramp a light bulb, a cross, a convex lens, and a screen.
2. Fix the positions of the screen and the cross (60-80cm apart).
3. Move the lens between the cross and the screen, and try to obtain the real
image of the cross on the screen.
4. Measure the object distance do (from the object to the lens)
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Algebra Based Physics
Geometric Optics
Investigating Converging Lenses - Guided
PSI Physics – Geometric Optics
5. Measure the image distance di (from the image to the lens)
6. Use the formula of the lens to determine the focal length f:
1
𝑓
= 1/𝑑o + 1/𝑑i
7. Calculate the magnification of the lens: m = di/do
8. Use the ruler to measure the height of the object and the height of the image.
Calculate the magnification of the lens theoretically: m = hi/ho
9. Change the distance between the cross and the screen, repear Steps 2-6 three
times. Record all numbers in Table 1.
10. Use your calculations to complete Table 2.
Data Collection
Table 1
Trial
Object
Distance
do, cm
Image
Distance
di, cm
Focal
Length
f, cm
Object
Height
ho, cm
Image
Height
hi, cm
Magnific
ation
m = di/do
Magnific
ation
m = hi/ho
1
2
3
Table 2
Position of
Object
Beyond 2f
Position of
image
Real or Virtual
Larger or
Smaller
Inverted or
Erect
Between f and
2f
At 2f
Between f and
the lens
Analysis
Predict the image formed if a source of light is placed between the center of curvature
and the focal point of a converging lens. Make sure to include a ray diagram that led to
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Algebra Based Physics
Geometric Optics
Investigating Converging Lenses - Guided
PSI Physics – Geometric Optics
your answer, and identify the three main characteristics of the image (upright/inverted,
real/virtual, larger/smaller).
Make conclusion about your major result.
njctl.org
Algebra Based Physics
Geometric Optics