Yanbu University College
PHYSICAL SCIENCE (PHSC101)
Lab. Exercise No. 8
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Refraction of Light through a Glass Slab
OBJECT:
 To verify law of refraction of light using a glass slab.
 Find the constant of refraction (refractive index) of glass.
 Determine the speed of light in glass.
MATERIAL REQUIRED:
A glass slab, A drawing board, Thumb pins, Common pins (optical needle),
Protector of least count 1o, Sharp pencil and rubber.
EXPERIMENTAL ARRANGEMENTS:
 Fix a drawing sheet on the drawing board using thumb pins at the four corners
of the drawing sheet
 Place the glass slab on the drawing sheet
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PHSC101, Lab-8
PROCEDURE:
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Draw the boundary of the glass slab ABCD using sharp Pencil carefully so that the slab is not
displaced during drawing.
Remove the glass slab.
Draw a normal on the face AB using protector.
Make an angle with the normal 30o using protector and draw incident ray IO the angle between
incident ray and the normal is called an angle of incidence i.
Fix two common pins on the incident ray IO such that the distance between them should be at least
5cm.
Replace the slab on its boundary.
See the image of these pin from the side CD and fix two more pins separated by 5cm such that all
the four pins are in one line (bases of the pins should be in line not their heads).
Circle the position of common pins nearer to side CD and then remove the pins join the circles so as
to draw a line IO/ that intersects the face CD of the slab called outgoing ray.
Now join points O and O/ thorough the glass slab.
Measure the angle which IO/ makes with the normal called
Angle of refraction r record in Table
1.
Repeat the experiment with angle of incident 35o, 40o.
OBSERVATIONS:
Angle of Incidence
i
Sini
Angle of Refraction
r
Sinr

Sin i
Sin r
30o
40o
50o
60o
Mean value of Refractive Index = µ = _____________
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PHSC101, Lab-8
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PHSC101, Lab-8
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PHSC101, Lab-8
CALCULATIONS:
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Find the Sine of Angle of Incidence and Angle of Refraction.
Find the ratio of Sini and Sinr .
Find the Refractive Index ‘µ’ by using the following expression:
Sin i

Sin r
Refractive Index can also be calculated by:
c

v
Where µ = Refracted Index of Glass = 1.5
c = Speed of Light in air = 3x108 m/s
v = Speed of Light in glass
Calculate the speed of light in glass by using this relation.
Result:
1. The angle of refraction is_____ than the angle of Incidence so it means the light bends
towards the normal on entering the glass which is called refraction of light.
2. The refractive index of glass is found as ________.
3. The speed of light in glass is found as ________ m/sec.
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PHSC101, Lab-8
Review Question:
Q.1 How you can say that light travels in a straight line when traveling through homogenous
medium.
Q.2 The bending of light is due to change in speed of light or change in wavelength of light.
Q.3 During fishing is it better to aim
a) on the fish
b) below the image of the fish
Q.4 In which medium the speed of light is maximum.
Q.5 If we keep a pencil in a glass full of water then the pencil appears to break from the middle
why?
End of the Exercise
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PHSC101, Lab-8