Fady Makram
Physics
Mr. Singh
1st March 2009
Lab Report
Aim of the experiment:
The aim of this experiment was to measure the refractive index of a given glass slab, in
this case a rectangular block.
Apparatus:
Light Box, paper, pins and a rectangular glass block.
Procedure:
I pinned the paper to the board using the flat head pins. I then turned on the power for
the light box and placed the glass block in front of the ray of light coming from the light
box. I placed a pin at the point of incidence and another on the incident ray and I then
connect the pins to form both the incident ray and the point of incidence. Then I placed
another two pins to form the emergent ray and the connected them with a pencil. I then
joined then two rays with a straight line.
I used a protractor and drew a normal, which is an imaginary line perpendicular to the
glass block at the point of incidence. I measured the angle of refraction, which is the
angle between the normal drawn at the point of incidence and the refractive ray. I
recorded the angle of refraction which was 14 degrees.
I used the same procedure to find the angle of incidence which was the angle between
the normal and the incident ray. I found the angle of incidence to be 19 degrees
Observations:
When the ray enters the glass block, it bends towards the normal and when it exists the
glass block, it bends away from the normal. This is because if a ray of light travels from a
rarer to a denser material, the ray bends towards the normal and when it travels from a
denser to a rarer medium, it bends away from the normal.
Data Collected and Mathematical Procedure:
I obtained the readings from my group and formed a table to get an average of the
results.
Using the mathematical formula Reflective Index =
𝐬𝐢𝐧(𝒊)
I filled out a table to form
𝐬𝐢𝐧(𝒓)
the results obtained from the lab.
Observation
#
1
2
3
4
Angle of
Incidence(i)
19
27
10
15
Angle of
Refraction(r)
14
19
8
13
Sin(i)
Sin(r)
0.326
0.434
0.174
0.259
0.242
0.326
0.139
0.225
RI =
sin(i)/sin(r)
1.346
1.294
1.248
1.151
I averaged all the refractive indexes I obtained to get the most suitable and reliable refractive
index which was found to be 1.28475
Conclusion:
In conclusion, we found that a ray of light passing from a rarer to a denser medium
bends towards the normal and if a ray of light travels from a denser to rarer medium the
ray of light bends away from the normal.