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# Refraction of Light by Water

Extracts from this document...

Introduction

Refraction of Light by Water and

Refraction of Water into Air

PURPOSE:

1. To investigate the refraction of light by water
2. To investigate the refraction of water into light
3. To develop Snell’s Law

MATERIALS:

Refer to pp.46-47 of Physics 11 Laboratory Manual.

Theory and Hypothesis:

When we observe a straw in water, the straw appears to be disjointed because we are used to seeing light in a straight line. According to Snell’s Law ( where 1 is the incident ray and 2 is the refracted ray), when light passes from a less dense to a more dense medium, the refracted ray should “bend” away from the normal; and when light is shot back from water into air, the refracted should “bend” toward the normal. This experiment should show us the results of Snell’s Law by producing observed angles similar to the calculated angles. If I graph Sin i against Sin R of light from air into water, I should produce a straight line whose slope should resemble the n2 value of Snell’s Law because n1 is the index of refraction of air, which is approximately 1.

PROCEDURES:

Refer to pp.46-47 of Physics 11 Laboratory Manual.

DATA AND OBSERVATIONS:

Middle

10.0°

13.0°

0.174 ± 0.034

0.225 ± 0.034

0.773 ± 0.014

refraction

3

20.0°

29.0°

0.342 ± 0.033

0.485 ± 0.031

0.705 ± 0.027

refraction

4

30.0°

40.0°

0.500 ± 0.030

0.643 ± 0.027

0.778 ± 0.033

refraction

5

40.0°

80.0°

0.643 ± 0.027

0.985 ± 0.006

0.653 ± 0.030

refraction

6

50.0°

Undefined (90.0°)

0.766 ± 0.022

undefined

undefined

reflection

7

60.0°

Undefined

0.866 ± 0.017

undefined

undefined

reflection

Calculations and Analysis

• Sample Calculation of Sin i

Table 1 Observation 5

Formula:

where i =  40.0°

Sin I     =

=

=0.643 ± 0.027

• Sample Calculation of Sin R

Table 2 Observation 3

Formula:

where i =  20.0°

Sin R   =

=

=0.485 ± 0.031

• Sample Calculation of Sin i/SinR

Table 1 Observation 8

Formula:

where x=Sin i

∆x=Uncertainty of Sin i

y=Sin R

∆y=Uncertainty of Sin R

Sin r         =

=1.22 ± 0.03

• Sample Calculation of Slope of Refraction of Light by Water

Conclusion

1. Above 50.0° at the boundary between water and the air, all the light is reflected.
1. At the critical angle 50.0°, the angle of refraction is 90.0° according to “Table 2 Observation 6”.

SOURCES OF UNCERTAINTY:

• Impurities in water and air will have caused the light to be refracted more than the expected theoretical values. As well, the index of refraction (n) for the two substances would be inaccurate.
• The plastic dish holding the water may have will have slightly refracted the light.
• Light from the ray box is completely focused and coherent, thus readings may be inaccurate.

CONCLUSION:

Light is refracted towards the normal when it passes from air into water and away from the normal when it passes from water into air because of a change in the medium’s density. The index of refraction of water (n=1.33) can be found by dividing the sin of the incident angle by the sin of the resulting refractive angle as shown in my sin i/sin R calculations. And if we reflect light by water and back into air again, the light will travel in the same direction as the original incident ray due to the inverse relationship of the indices of refraction as shown in my analysis.

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