Name ______Period _____

Lab Partners ______

______

______

Lab: Determining the Characteristics of Convex Lens Images

Purpose: To study the images formed by light passing through a convex lens when the object (a light) is

placed at 5 different distances from the lens.

Testable Question: Can we use the lens and magnification equations to give us realistic values for the

image distances and magnifications produced by a convex lens of known focal length?

Procedure:

Part I

§  Find the focal length f of your lens by letting light coming from the hallway or yard outside the window (far away) pass over your shoulder, through the lens, and onto a screen. Focus the image on the screen and measure the distance from the sharp image to your lens. Record this distance in centimeters as the focal length f on your data table.

§  Measure the actual size So of the object (light source) in centimeters. Record this size on your data table.

§  Place the light at each of the object distances indicated on the data table below, and move the screen until you get a clear image of the object (the light) on the screen.

§  Measure and record the object distance do, image distance di and the image size Si in centimeters and image orientation (upright or inverted) for each position on your data table.

§  If you cannot focus a clear image on the screen, the image is either virtual or there is no image formed at all. Look through the lens directly at the object (the light) to see the image.

§  Calculate (and show a sample of each calculation on the Sample Calculations table following the data table:

o  the image distance di ,

o  the % difference between the measured and calculated image distances,

o  the magnification M = Si / So

o  the magnification M = -di / do

o  the % difference between the measured (Si / So) and calculated (-di / do) magnifications

Part II

§  Obtain another convex and a concave lens. Try to find two combination that makes a telescope when you view distant objects such as a tree out a window. Make sketches in the box below the data table of the lens combinations that are successful, showing where your eye is and how far apart the lenses are.

§  Important! Answer question # 1 before you put away the lab materials.

Materials: meter stick, convex lens, index card screen, ruler, lens holder, screen holder, light source, meter

stick stand

Data Table: focal length of lens f (cm) ______size of object(light) So (cm) ______

Object position from lens / do
(cm) / di measured
(cm) / di
calculated
(cm) / %
Difference
of di
Values / Si
(cm) /

M

measured
(Si/So) / M
calculated
(di/do) / %
Difference
of M Values / Image
Orientation

Beyond 2f

At 2f

Between f
and 2f
At f
Inside f

Sample Calculations:

Quantity calculated / Formula Used / Substitution using your data / Answer with Units
Calculated Image distance di
% Difference of di Values
Mmeasured = (Si/So)
Mmeasured = (di/do)
% Difference of M values

Questions:

1. What do you predict would be the effect on the image viewed through a telescope if the area of the lens

closest to the object were reduced by half? Perform the experiment by covering half of the lenses closest

to the object viewed through your telescope.(The lens closest to the object you are viewing, not the lens

closest to your eye).

2. Under what conditions is an image from a convex lens:

§  Inverted? ______

§  Upright? ______

§  Real? ______

§  Virtual? ______

§  Larger than the object? ______

§  Smaller than the object? ______

3. A simple camera system consists of an opening that allows light in, a convex lens, and photographic film or

paper placed where the image of the object is formed. Draw a ray diagram explaining how a camera allows us

to produce images of objects that are smaller in size that the objects themselves.

4. Will the image produced on the film by the camera be upright or inverted? ______

5. A movie projector system consists of a light that shines through some film, then passed through a lens to

produce a very much enlarged image on a distant screen. Draw a ray diagram explaining how a projector

allows us to produce images of objects that are larger in size that the objects (the film images) themselves.

6. Will the image produced on the screen by the projector be upright or inverted? ______

7. Compare your measured values for the image distance di and the magnification M to the values you found

using the equations. What do your results seem to indicate about the validity of the equations?

Why do you think this way?

8. Describe and EXPLAIN the EFFECT of three possible reasons why your measured values for di were

different from your calculated values.

· 

· 

9. Is there something wrong with assuming that the focal length of the lens is the measurement from the lens to

the sharp image formed of light coming from a distance? If no, why not? If yes, why yes?

10. Bonus! Do a ray diagram illustrating how the telescope lens arrangement you found works to magnify

a distant object you are looking at.

11. Complete the ray diagrams to find the images for each of the objects shown in front of the lenses below,

showing the image and its orientation. Describe each image in terms of whether it is real or virtual, reduced

or enlarged, upright or inverted.