Lab & Pre-lab #11

Lenses and Images v 0.1
Step 5: Measure the height of the image, h i , and the height of the object, h o , and record these.
Also note whether the object is inverted or erect. Then calculate the ratios of the image
and object heights, and the image and object distances.
measured: h i = cm measured: h o = cm
measured: h i /h o = measured: d i /d o =
Question 1.6 Is the ratio of the measured heights of the image and object nearly equal
to the ratio of the measured distances Again, discuss the accuracy with which you could
measure these quantities to draw a fair conclusion about their equality.
There is an algebraic equation that relates the object distance, d 0 , (the distance from
the lens to the object), the image distance, d i , (distance from lens to the position of the
image), and the focal length, f, of the lens. This relationship involves the power of the
lens, which is inversely proportional to the focal length (shorter focal length means greater
power).
1
+ 1 = 1 thin lens formula
d o d i f
.
Question 1.7 Using the formula above calculate the image distance given that f = 15cm,
and d o = 20cm. Compare this with your measured value, again taking into account the
precision in your measurement of the image and object distances.
Measured: d i =
cm.
Prediction 1.2 What will happen if the distance from the lens to the object is increased
Will the image distance get shorter or longer Will the image get larger or smaller To
make this prediction, make a ray diagram with the object farther from the lens than the
previous one. A scale drawing is provided in Fig. 7.
Now test your predictions.
Step 6: Move the lens so that it is at least 30cm from the F-diaphragm.
Step 7: Move the white screen until you find a position at which a clear image is formed.
Step 8: Measure the object and image distances, and the height of the object and image.
Record the measurements below.
d i = cm d o = cm
h i = cm h o = cm
PHYS-204: Physics II Laboratory 7