Angel De Leon
11/5/2010
Science-Labreque
Investigating Light Intensity
Problem: How does light intensity change with the distance from the light source?
Background Information: When I watch TV there is a big light that shines. Also when
I eat dinner, there is a big circular light on the ceiling and shines upon us while we
eat. The light is big enough to shine throughout the whole room.
Materials:
2-meter sticks
Light probe
Flashlight
Tape
Method:
1) In the dark water part of the room, secure the flashlight to the table with
tape, so that the light shines away from the window.
2) Secure two-meter sticks to the table with tape about 1cm apart, so they form
smooth path in front of the light.
3) Turn on the light probe and place it directly in front of the flashlight. Record
the reading.
4) Take a reading at 10cm intervals up to 1m.
5) Repeat for a total of three trials.
Observations: While we did the experiment, Investigating Light Intensity, this
experiment taught me several things. I observed that the closer the probe is to the
flashlight, the number on the probe (light intensity) increases. Conversely, when it
gets farther from the flashlight, the light intensity decreases. Basically if it is darker
the light intensity will decrease but if there is light the light intensity will increase.
When my group did trial one, two to four numbers were in the same range and the
reason for that is that it was positioned in the same place.
My partner spotted a mistake on the 50 cm part, the light intensity increased.
We knew something was wrong. Then he looked at the window and he suggested
that this was the cause of the sunlight. I then looked at the window and realized that
this must be the problem. We both waited for a minute for the sun to die down and
then the pattern continued as usual. For both trials two and three the weather was
cloudy which made the pattern a bit more linear.
Distance
(cm)
10
20
30
40
50
60
70
80
90
100
Trial 1
0.966
0.599
0.305
0.19
0.13
0.091
0.072
0.058
0.05
0.042
Trial 2
0.969
0.556
0.284
0.18
0.127
0.095
0.077
0.061
0.052
0.043
Trial 3
0.973
0.594
0.31
0.196
0.133
0.099
0.079
0.063
0.052
0.045
Average
0.969
0.583
0.299666667
0.188666667
0.13
0.095
0.076
0.060666667
0.051333333
0.043333333
Investigating Light Intensity
1.2
Light Intensity
1
0.8
Trial 1
0.6
Trial 2
0.4
Trial 3
0.2
Average
0
1
2
3
4
5
6
7
Distance (x10cm)
8
9
10
Conclusion:
A. The average of the whole Light Intensity is shown above in purple. In general,
the average for all three trials is 0.249. The average on the graph shows that
when you move your light probe to a further distance from the flashlight, the
light intensity decreases.
B. I observed that when you do the next two trials the light intensity for the first
trial decreases. I think since my partner and I were right next to the window,
maybe the sunlight affected the flashlight’s light intensity. When we did the
experiment at trial one, it was very sunny. Though when we did trial 2 and 3
the weather became cloudy outside. Also I noticed that from all the trials the
light intensity decreased. The further your probe is from the flashlight, the
lower intensity you get but, when you get closer to the flashlight the higher
intensity it will be.
C. The only thing that was repeated was doing the trials. We had to do three
trials. When I put the probe to 50 cm that was when my partner and I were
sure that the further you go, the lower intensity you get. Also one evident
pattern is that the numbers from our table declines.
D. From the very beginning, when we started trial one, I then noticed that when
you get closer to the flashlight it will be a higher intensity and if you are
farther from the flashlight it will be a lower intensity. The relationship among
the light intensity and distance is that when you move the light probe closer,
the higher intensity you will get. Though the opposite thing happens when
you move the light probe farther, the light intensity will be lower.
E. I think the first reason is that the atoms of the electromagnetic waves
scatters and the further it goes the atoms from the electromagnetic waves
will disperse more. The atoms will never disappear. I think the second reason
is that anyplace you put the probe; there will always be some light intensity.
Even if there is just a little like wood. Constantly there will always be a
number on the light probe.
References:
Our Worksheet for this Experiment
Mr. Labreque