-
7/29/2019 Converging Lenses Experiment Report
1/4
Converging Lenses Experiment Report
Introduction
This experiment was designed to find out more about the
relationship between the distancebetween the lens and an image
source, u, and the distance between the lens and the screen
when
the image shown is focused, v. This should also depend on the
lens focal length due to the Lens
Maker equation which is as follows:
When f = lens focal length / metres, u = distance between lens
and source / metres and v = distance between lens and screen /
metres
Using the same measurements, this experiment should also be able
to show the power in dioptres of
the lens being used via this equation:
When f = lens focal length / metres and p = power of lens /
dioptres
Method and Diagrams
The independent variable of this experiment was the distance
between the lens and the image
source, u. The method would therefore have to reflect this a use
the difference in u to measure thecomparative change in the
dependant variable, v. This experiment should use this set up:
To make sure this experiment is reproducible, each experiment
should be done at least 3 times. This
will also allow you to create averages from the data you collect
for plotting on graphs. In order to
ensure a fair test a few precautions must be in place.
- The lens and metre sticks must not be moved throughout one set
of results.- The point of both the screen and the bulb at which you
take the measurement must be the
same for each result.
-
7/29/2019 Converging Lenses Experiment Report
2/4
- The light intensity of the bulb must remain as similar as
possible.Here is the method used to gather data for this
experiment:
1. Place the lens holder at the 0 on both metre sticks and turn
on the bulb.2.
Move the bulb to the measurement of u you are currently trying
to measure.
3. Adjust the screens position until a focused image in shown on
the screen.4. Measure the distance from the screen to the lens
using the metre stick. Take this value
down.
5. Repeat steps 1 5 for a different measurement of u.
Results
The experiment was carried out three times over to check if the
results were reproducible. Then thedata was used to calculate an
average of the results using each of the three tests.
As you can see, the data was processed to give the values of
,
,
and(
). These would later
help in the calculations of the focal length and the power of
the lens. The averages that were
calculated can be used to formulate graphs as you will see in
the next part of this report. However
the data shows the uncertainty of each experiment in the form of
a range between the lowest data
value and the highest.
This uncertainty could have come from many sources, most of
which were highlighted when talking
about fair tests in the Method section of this report. The main
problem in this experiment wasjudging by eye when the image on the
screen was in focus before taking down the measurement.
This was a problem because it meant the results could have been
about 2cms out on some results,
and they could have been more accurate with better
equipment.
-
7/29/2019 Converging Lenses Experiment Report
3/4
Graphs
All graphs produced using the data show on the previous page
have used the Cartesian Convention,
meaning that all results of u, because they were behind the
lens, were taken as negative values and
plotted accordingly. In these graphs the uncertainty of each
point was unable to be shown on the
graphs. However this has been considered in the analysis of the
data.
Using this data, a graph of the relationship between the value
of u and the average of the values of v
was plotted. This shows us that there is a relationship that
could follow an equation similar to as the graph produced shows an
asymptote.
0.00
0.10
0.20
0.30
0.40
0.50
0.60
0.70
0.80
-0.8 -0.7 -0.6 -0.5 -0.4 -0.3 -0.2 -0.1 0
Distancebetweenthelensa
ndthe
buld/m
Distance between the lens and the focused image / m
Graph showing relationship between distances v and
u
0.00
1.00
2.00
3.00
4.00
5.00
6.00
-6.00 -5.00 -4.00 -3.00 -2.00 -1.00 0.00
1/v
1/u
Graph showing the relationship between 1/v and 1/u
-
7/29/2019 Converging Lenses Experiment Report
4/4
As you can see from the graph on the previous page, the values
of and
negatively correlated to
each other, shown by the dropping trend line produced by the
data.
From the data, we can also take an average of the ( )and use it
to find the lens supposed focal
length. After calculations this came out to be, in the case of
this lens:
Discussion
The first graph produced shows us a relationship between u and v
that suggests that as u gets larger,
the distance needed to change v by in order to get a focused
image becomes smaller. You can also
see the point at which distance v is converging to is the lens
focal length or thereabouts. This proves
the idea that if you were to use the equation
and change u to a distance very far away from the lens, which we
could call , you would end upwith a value of the focal length as
v.
You can also see from the second graph that there is a very
strong correlation between the values of and
. This illiterates the fact that the greater the distance u, the
smaller the distance v. You should
also be able to understand that using this relationship, the
point at which both values are equal
should be the same as the focal length of the lens.
