By Osura Jayasundara
Stage 1 Physics
Snell’s Law Summative Practical
Investigation
When light moves between two transparent media, at an angle to the junction, the light
changes direction. Snell’s law states that the ratio of the sine of the angle of refraction to
the angle of incidence is a constant for any given pair of media. This law is used to
determine the direction of light rays through refractive media with varying indices of
refraction.
𝑆𝑖𝑛∅1
= 𝐶𝑜𝑛𝑠𝑡𝑎𝑛𝑡
𝑆𝑖𝑛∅2
Aim: To verify Snell’s law for the air into Perspex interface using the apparatus provided
Table of experimental results of the ray tracings
Θi
ΘR
SinΘi
SinΘr
5°
10°
15°
20°
25°
30°
35°
3°
6°
9°
12°
16°
19°
22°
.08715
.1736
.2588
.3420
.4226
.5
.5735
.0523
.1045
.1564
.2079
.2756
.3256
.3746
Graph (Θi Vs Θr)
Θr Vs ΘI
25
20
15
ΘR Vs ΘI
Linear (ΘR Vs ΘI)
10
5
0
5
10
15
20
25
30
35
ΘI
5
10
15
20
25
30
35
ΘR
3
6
9
12
16
19
22
Graph SinΘi Vs SinΘr
SinΘi Vs SinΘr
SinΘr
SinΘi
0.0523 0.08715
0.1045 0.1736
0.7
0.6
0.1564
0.2079
0.2756
0.3256
0.3746
0.5
0.4
SinΘi Vs SinΘr
0.3
0.2588
0.342
0.4226
0.5
0.5735
Linear (SinΘi Vs SinΘr)
0.2
0.1
0
-
The slope of graph =
=
𝑆𝑖𝑛∅𝑖
𝑆𝑖𝑛∅𝑟
(.2756− .1045)
(.4226− .1736)
=0.6871
-
Points used (.1736, .1095), (.4226, .2756)
The slope of 0.6871 shows the steepness of the line SinΘi vs. SinΘr. This shows
the trend and relationship with the ray tracings. It also shows the gradient of the
constant in this graph Sini over Sinr and the same constant as the gradient of the
graph speed of light in air/ Speed of light in the medium. The constant is the
speeds of light in the two media.
Angle of Incidence
Angle of
Refraction
SinΘI/SinΘR
Constant
Refractive Index
Sin5°= .08715
Sin10°=.1736
Sin15°=.2588
Sin20°=.3420
Sin25°=.4226
Sin30°=.5
Sin35°=.5735
Sin3°=.0523
Sin6°=.1045
Sin9°=.1564
Sin12°=.2079
Sin16°=.2756
Sin19°=.3256
Sin22°=.3746
.08715/.0523
.1736/.1045
.2588/.1564
.3420/.2079
.4226/.2756
.5/.3256
.5736/.3746
Average=
1.66
1.66
1.65
1.64
1.53
1.53
1.53
1.6
Conclusion
Do your results to verify Snell’s Law.
The results from this experiment show that Snell’s law works providing correct
measurements and calculations are put in place. In the experiment completed, the results
were found to be a bit inaccurate when considered with that of Snell’s law. Overall there
was an average refractive index of 1.6 which is .12 over the average mark. So therefore this
law provided does work if precise measurements and calculations are worked out.
State the value of the constant
The constant refractive index of Perspex is 1.48, which is very close to the refractive index
attained in this experiment.
Evaluation
How accurate were your results?
In order to obtain satisfactory results, it is a must to concentrate more on finding the
accurate refraction degree. The results were slightly inaccurate due to the fact that not
much effort put into getting the ray light on a straight line accurately. If the effort was put
on to this the results would have been greatly increased.
What limited the precision (accuracy)?
The accuracy was slightly limited by precision of where points entered through the Perspex.
The naming of the angles was also something which proved to be quite an effort, as
retrieving exact measurements was something which was divisive as in individual activity.
How could you improve the precision?
In order to improve accuracy patience must be taken when considering the angles and when
putting the ray light in a straight line at which intersections occur and how far apart each of
the refracted rays are from each other in terms of angles.
Research – Application Questions
𝑆𝑖𝑛∅1 𝑣1
𝑛2
=
=
𝑆𝑖𝑛∅2 𝑣2
𝑛1
What do v1, v2, n1 and n2 refer to?
N=c/v where c is the speed of light in a vacuum and v is the speed of light in the medium,
Also the ratio n2/n1 is called the relative index of refraction.
V= referred as the velocity of light in respective medium.
What is the refractive index of a material? Explain
The refractive index of a material is the measure of speed of light in that substance, In other
words it is a way of measuring the velocity at which a material is able to pass through a
mediums refractive index. It is expressed as a ratio of the speed of light in vacuum relative
to that in the considered medium. This can be defined as speed of light in material 1/speed
of light in material 2. This also measure the bending of a ray of light when passing from one
medium to another.
If light was to travel from water (refractive index 1.33) into cubic zirconia (fake diamond,
refractive index of 2.15) calculate the value of (SinΘ ‘i’/ SinΘ ‘r’) for this interface. If the
angle of incidence was 45° what would the corresponding angle of refraction be?
Cubic Zirconia Refractive Index= 2.15
Water Refraction Index= 1.33
1.33xSin (45)/2.15= SinΘr
N1SinΘi=N2SinΘr
1.33xSin (45) = 2.15xSinΘr
SinΘr=0.4374195437
Θr=26°
Repeat the previous question but for an Ethanol/diamond interface. State where you
found your values (Ethanol is also called ethyl alcohol).
Ethanol Refractive Index= 1.36
Diamond Refractive Index= 2.42
1.36xSin (45)/2.42=SinΘr
SinΘr=0.3973823233
N1SinΘi=N2SinΘr
1.36xSin (45) =2.42xSinΘr
Θr= 23°
In text References
RefractiveIndex.INFO - Refractive index database. 2011. RefractiveIndex.INFO - Refractive
index database . http://refractiveindex.info/. [Accessed 29th May 2011].
Refractive Index n.d., , accessed 16 June 2011,
<http://www.matter.org.uk/Schools/SchoolsGlossary/refractive_index.html>.
Snells law n.d., , accessed 16 June 2011,
<http://www.sasked.gov.sk.ca/docs/physics/u3c12phy.html>.