1

REFRACTION OF LIGHT

THROUGH PLAN PARALLEL GLASS

A. PURPOSE OF EXPERIMENT

There are some purposes which want to be achieved from this experiment.

1. Determining the value of the index of refraction of plan parallel glass.

2. Determining the value of the shift between the coming light and light of

refraction out of plan parallel glass.

B. TOOLS AND MATERIALS

Here are the tools and materials needed in order to do this experiment.

1. Box of Light (Ray Box)

2. Protractor (SSN = 1o)

3. Plan Parallel Glass

4. Pencil

5. Ruler (SSN = 0.1 cm)

6. HVS Paper (White Paper)

C. FUNDAMENTAL THEORY

Refraction of light is a phenomenon of the light propagation direction

changing since the light passes the two different mediums. The refraction of

light occurs when a beam comes from the air toward the water and vice versa.

Generally, refraction of light occurs when the light comes from a wide apart

medium toward the closer medium and vice versa. Snellius law, in relation

with light refraction, states that:

1. The coming ray, the refraction ray, and the normal line are intersecting at

one point and on a flat surface.

2. The relationship among the coming angle and the refraction angle is stated

as follow.

2211 sinsin nn

Where:

1n The refraction index of medium 1

2

2n The refraction index of medium 2

1 The coming angle

2 The refraction angle

A beam which travels from a small density medium toward the bigger density

medium will be refracted close to the normal line, then the coming angle

would be bigger than the refraction angle. In contrary, if a beam travels from a

big density medium toward the smaller density medium, it will be refracted

avoiding the normal line, then the coming angle would be smaller than the

refraction angle. If a coming ray from the air passes the plan parallel glass as

shown by figure 1, the direction of coming ray would be parallel with the

direction of refraction ray, but it shifted as t. The value of t can be determined

by the following equation.

r

ridt

cos

sin

Where:

t = the displacement of ray

d = the thickness of plan parallel glass

i = coming angle

r = refraction angle

Figure 1. The scheme of light refraction through plan parallel glass

d

N

A

B

t

D

i

r

i r

C

d

3

D. EXPERIMENT METHOD

The following are the experiment method that should be done in order to do

this experiment.

1. Setting up the tools and materials as the following picture.

2. Measuring the thickness of plan parallel glass by ruler.

3. Drawing lines with angle 10°, 25°, 40°, 55°, and 70° with axis line PQ on

the paper.

4. Setting the position of ray box to make the coming ray exactly on the line

drawn at 10° through PQ. Then, the angle of coming ray is 10°.

5. Investigating the refraction ray and marking its direction by a cross mark

at diffraction ray. Getting up the plan parallel glass, and then drawing the

refraction ray. Where, it will be gotten two angles of refraction, there are r1

(the angle of refraction for the air-glass refraction) and r2 (the angle of

refraction for the glass-air refraction). Noting the recorded data in

providing table.

6. Repeating the steps 4 and 5 for other coming angles.

7. Recording the result data in following table.

The thickness of glass (d) =…………

No Coming ray (i1) Refraction ray 1

(r1)

Refraction ray 2

(r2)

1

2

…..

Ray Box

Plan Parallel Glass

To the source of voltage

HVS Paper

P

Q

4

E. DATA ANALYSIS TECHNIQUE

The following are the analysis technique used in order to analysis the data

recorded from the experiment.

1. Determining the refraction index of plan parallel glass (n2).

2211 sinsin nn

Where:

1n The refraction index of medium 1 (air)

2n The refraction index of medium 2 (glass)

1 The coming angle

2 The refraction angle

2. Determining the value of n of the refraction index of plan parallel glass.

yy

xx

yn

2

1

3. Stating the refraction index of plan parallel glass in the following form.

n = n n

4. Determining the relative error (RE) of refraction index of plan parallel

glass.

%100

n

nRE

5. Determining the value of the displacement of coming ray and refraction

ray that travel out the glass (t).

r

ridt

cos

sin

Where:

t = the displacement of ray

d = the thickness of plan parallel glass

i = coming angle

r = refraction angle

5

6. Determining the value of t of the displacement of coming ray and

refraction ray that travel out the glass.

dyy

dxx

y

dd

y

xt

2

7. Stating the refraction index of plan parallel glass in the following form.

t = t t

8. Determining the relative error (RE) of displacement.

%100

t

tRE

F. DATA OF EXPERIMENT

No Incident Angle (i) Refractive Angle 1 (r1) Refractive Angle 2 (r2)

1 10.00 6.5

0 9.7

0

2 25.00 17.5

0 25.0

0

3 40.00 26.5

0 39.7

0

4 55.00 34.5

0 55.2

0

5 70.00 40.1

0 69.0

0

G. DATA ANALYSIS

No Coming

Angle (i)

Refraction

Angle 1

(r1)

Refraction

Angle 2

(r2)

Sin i

(X)

Sin r1

(Y) X/Y

1 10.00 6.5

0 9.7

0 0.17 0.11 1.54

2 25.00 17.5

0 25.0

0 0.42 0.30 1.40

3 40.00 26.5

0 39.7

0 0.64 0.45 1.42

4 55.00 34.5

0 55.2

0 0.82 0.57 1.44

5 70.00 40.1

0 69.0

0 0.94 0.64 1.46

Jumlah 2.99 2.07 7.27

6

1. Determining the refraction index of plan parallel glass (n2).

2211 sinsin nn

45.1

5

27.7

n

n

N

nn

2. Determining the value of n of the refraction index of plan parallel glass.

59.0

5,007.2

99.25,0

2.07

1

1

1

2

2

2

n

n

yy

xx

yn

yy

xx

yn

yy

nx

x

nn

3. Stating the refraction index of plan parallel glass in the following form.

n = n n

n = 45.1 0.59

4. Determining the relative error (RE) of refraction index of plan parallel

glass.

%100

n

nRE

%10045.1

59.0RE

%58.40RE

7

No Coming

Angle (i)

Refraction

Angle 1

(r1)

Coming

Angle –

Refraction

Angle (i-r)

Sin i-r

(X)

Cos r1

(Y) X/Y

1 10,00 6,5

0 3,5 0,06 0,99 0,06

2 20,00 13,0

0 7,0 0,12 0,97 0,12

3 30,00 19,0

0 11,0 0,19 0,94 0,20

4 40,00 26,0

0 14,0 0,24 0,89 0,26

5 50,00 31,0

0 19,0 0,32 0,85 0,37

Jumlah 0,93 4,64 1,01

5. Determining the value of the displacement of coming ray and refraction

ray that travel out the glass (t).

d = 6.0 cm

d = 6.0 x 10-2

m

According to the fundamental theory, the displacement of coming ray and

refraction ray that travel out the glass is as follow.

r

ridt

cos

sin

If the value of sin (i-r) is represented by X, and the value of cos r is

represented by Y, then the equation above would be as follow.

Y

Xdt

a. The displacement for the 10,00 coming angle

1) Determining the value of 𝑡

mxt

xxt

Y

Xdt

2

2

1037.0

06.0100.6

2) Determining the value of ∆𝑡

Y

Y

X

X

d

dt

8

mt

xt

dyy

dxx

y

dd

y

xt

dyy

nx

x

nd

d

nt

2

2

2

10035,0

5,0994,0

061,006,05,0

994,0

06,005,0

994,0

061,0

3) Determining the value of relative error (RE)

00

00

00

53.9

10037.0

035.0

100

KR

xRE

xt

tRE

b. The displacement for the 25,00 coming angle

1) Determining the value of 𝑡

mxt

xxt

Y

Xdt

2

2

1081.0

13.0100.6

2) Determining the value of ∆𝑡

Y

Y

X

X

d

dt

mt

xt

dyy

dxx

y

dd

y

xt

dyy

nx

x

nd

d

nt

2

2

2

10042,0

5,095,0

13,006,05,0

95,0

06,005,0

95,0

13,0

3) Determining the value of relative error (RE)

9

00

00

00

20.5

10081.0

042.0

100

RE

xRE

xt

tRE

c. The displacement for the 40,00 coming angle

1) Determining the value of 𝑡

mxt

xxt

Y

Xdt

2

2

1056.1

26.0100.6

2) Determining the value of ∆𝑡

Y

Y

X

X

d

dt

mt

xt

dyy

dxx

y

dd

y

xt

dyy

nx

x

nd

d

nt

2

2

2

1005,0

5,089,0

23,006,05,0

89,0

06,005,0

89,0

23,0

3) Determining the value of relative error (RE)

00

00

00

5.3

10056.1

05.0

100

RE

xRE

xt

tRE

d. The displacement for the 55,00 coming angle

1) Determining the value of 𝑡

mxt

xxt

Y

Xdt

2

2

1054.2

42.0100.6

10

2) Determining the value of ∆𝑡

Y

Y

X

X

d

dt

mt

xt

dyy

dxx

y

dd

y

xt

dyy

nx

x

nd

d

nt

2

2

2

1007,0

5,082,0

35,006,05,0

82,0

06,005,0

82,0

35,0

3) Determining the value of relative error (RE)

00

00

00

8.2

10054.2

07.0

100

RE

xRE

xt

tRE

e. The displacement for the 70,00 coming angle

1) Determining the value of 𝑡

mxt

xxt

Y

Xdt

2

2

1090.3

65.0100.6

2) Determining the value of ∆𝑡

Y

Y

X

X

d

dt

mt

xt

dyy

dxx

y

dd

y

xt

dyy

nx

x

nd

d

nt

2

2

2

1009,0

5,076,0

49,006,05,0

76,0

06,005,0

76,0

49,0

11

3) Determining the value of relative error (RE)

00

00

00

5.2

10090.3

09.0

100

RE

xRE

xt

tRE

H. DISCUSSION

According to the data analysis of the experiment, it is retrieved the following

results.

a. Refraction index of plan parallel glass

1) Index of refraction is n = 45.1 0.59

2) Relative Error is 40.58%

b. The displacement of coming ray and refraction ray that travel out the

glass (t).

Coming Angle Displacement Relative Error

10.0° 0.37 ± 0.035 × 10−2𝑚 9.5% (acceptable)

25.0° 0.81 ± 0.042 × 10−2𝑚 5.2% (acceptable)

40.0° 1.56 ± 0.055 × 10−2𝑚 3.5% (acceptable)

55.0° 2.54 ± 0.073 × 10−2𝑚 2.8% (acceptable)

70.0° 3.90 ± 0.097 × 10−2𝑚 2.5% (acceptable)

It is believed that there are some errors that estimated inflence to the final of

this experiment.

1. Common Error

Common error is error that occurs because of the human error. The

common error of this experiment is the parallax error in the reading

scale of the protractor to find the angle. Error in drawing sketches of

the plan parallel glass in the HVS paper, and error when pointed the

incident light and the refractive light, because the light that out from

the collimator is too width its so influence the result of this experiment

are not same as the theory.

12

2. Systematic Error

Systematic error is an error that occurs because of the instruments used

as the influence of the environment at the time of trials The systematic

error of this experiment is might be caused by the potractor which

didn’t work well because it’s too dark, then it is hard to read the scale,

so its influence the result of this experiment.

3. Random Error

Random error is an error which the causing factors are uninvestigated.

The random error of this experiment is vibration of air, etc in drawing

the line and using the instruments.

I. CONCLUSION AND SUGGESTION

1. Conclusion

Based on the results of the experiment and the discussion above, it can be

summed up as follows.

a. Refraction index of plan parallel glass

1) Index of refraction is n = 45.1 0.59

2) Relative Error is 40.58%

b. The displacement of coming ray and refraction ray that travel out the

glass (t).

Coming Angle Displacement Relative Error

10.0° 0.37 ± 0.035 × 10−2𝑚 9.5% (acceptable)

25.0° 0.81 ± 0.042 × 10−2𝑚 5.2% (acceptable)

40.0° 1.56 ± 0.055 × 10−2𝑚 3.5% (acceptable)

55.0° 2.54 ± 0.073 × 10−2𝑚 2.8% (acceptable)

70.0° 3.90 ± 0.097 × 10−2𝑚 2.5% (acceptable)

c. There are some errors influences through this experiment. They are

common errors, systematic errors, and random errors as explained

before.

13

2. Suggestion

The suggestion that can be provided to the readers and other human in

order to do the same experiment is checking the necessary equipment. Do

the tool and the material taken or provided is still eligible to use or could

still be used or not. If actually it still can be used, then use them with well,

but if the tool used is not good, its recommend to replace it with the good

others because it will affect the final results of the experiment. It is also

important to pay attention in setting up the instrument to get the best

result.

REFERENCES

Suardana, I Kade. 2007. Petunjuk Praktikum Laboratorium 3. Singaraja:

Undiksha.

www.physicsclassroom.com/refraction for plan parallel glass (accessed on

December 5th, 2012)