VERIFICATION OF SNELL’S LAW OF REFRACTION
Materials Required : Glass slab, laser, protractor, paper
Research Question
What is the relationship between the angle of incidence and the angle of refraction
with respect to sine’s law ?
Independent Variable - Angle of Incidence
Dependant Variable - Angle of Refraction
Controlled Variable - light source (laser) , thickness of glass slab
Hypothesis
sin 𝑖
If the angle of incidence changes, then
will remain constant as stated by Snell’s
sin 𝑟
Law.
PROCEDURE
Place a glass slab on a flat sheet of paper and draw four straight lines around the slab
in to register the location of the slab on the paper. Shine a laser at the glass slab so it
emerges on the opposite side. Mark two dots on the incident ray and exit ray. Lift the
slab and complete all lines including the normal. Measure the angle of incidence i
and angle of refraction r using the protractor.
Repeat for different values of i. It is a good idea to start with a smaller angle of incidence and measure the corresponding angle of refraction. Then, gradually increase
this angle at approximately regular intervals to ensure a wide range of values. Draw
up a table like the one below. Plot a graph of sin i against sin r. A straight line
through the origin verifies Snell’s law of refraction i.e. sin i ∝ sin r. The slope of the
line tells us the value for the refractive index of glass. The refractive index of glass is
also equal to the average value of sini/sin r.
Precautions :
Lasers can cause damage if pointed towards the eye, so ensure they are handled with
care. When using the glass slab, ensure you do not drop it.
Raw Data Table :
This is the data that has not been changed or processed since acquisition.
Corresponding
Average Angle
Angle of Refraction of Refraction
S.N Angle of Incidence
(r) (Degrees) (All
(r) (Degrees)
o
(i) (Degrees)
figures are rounded (All figures are
off)
rounded off)
Trial Trial
1
2
Trial
3
1.
10
6
7
5
6
2
20
12
15
12
13
3.
30
20
22
19
20
4
40
32
29
30
30
5.
50
31
32
33
32
Processed Data:
This is the processed data we have obtained by calculating sin times the angle of incidence/ angle of refraction.
Ensure, when calculating you enter sin times angle in degrees.
S.No
Sin i (no unit) (all figures are rounded
off)
Sin r (no u
off)
1.
0.17
0.1
2.
0.34
0.22
3
0.5
0.34
4.
0.64
0.5
5.
0.77
0.53
0,8
Snells Law Verification
0,4
0,5; 0,3
0,34; 0,2
0,2
Sin r(no unit)
0,6
0,77; 0,5
0,64; 0,5
0,17; 0,1
-0,2
0,
0,; 0,
0,
0,2
0,4
0,6
Sin i(no unit)
0,8
1,
The
graph
passes
through
the origin
has a
positive
gradient
and confirms
Snells
Law, I.E,
the ratio
of sin
i/sin r is a
constant.
The angle of incidence is the independent variable, which is why it is represented on
the X axis and the angle of refraction is the dependent variable, depicted on Y axis.
As mentioned earlier, sin i/sin r would give us the refractive index of glass. The slope
of this graph (found by y2-y1/x2-x1) is sin r/sin i, which we find by using points
(0.34, 0.22) and (0.17, 0.1) which gives us 0.71 approx. To now find the refractive index, we must take the reciprocate the gradient which gives us 1.41 approx. This confirms n or the refractive index of glass, which is according to http://hyperphysics.phy-astr.gsu.edu/hbase/Tables/indrf.html, 1.52.
Conclusion :
My hypothesis has been proven correct as even after taking 5 varying angles of incidence and measuring its angle of refraction, I found sin i/sin r to be a constant value
of approximately 1.5 .
Evidence of the same has been given below using three varying angles of incidence :
• 0.5/0.34 = 1.47
• 0.77/0.53 = 1.45
• 0.34/0.22 = 1.54
This confirms Snells Law which states that the ratio of the sines of the angles of incidence are constant when it passes between two given media, and confirms the value
of 1.5 as the refracting index of glass.
Evaluation :
• When calculating the gradient of the graph, I got 1.41 instead of the expected answer of 1.5, these errors could be minimised by measuring the gradient with three
different sets of points, and calculating the average.
• There might have been errors when measuring the angle of incidence and angle of
refraction, as we are limited to calculating 1 degree intervals on the protractor.
• Additionally, even a slip of the hand or protractor when measuring the angle of refraction could lead to inaccurate data.
Referencing :
“IGCSE Physics Refraction Experiment.” Scribd, Scribd,
www.scribd.com/doc/135561521/IGCSE-Physics-Refraction-experiment.