Morehouse College

Optics Lab Snell’s Law

Dr. Searles

2/21/13

I.

Introduction

Refraction is the bending of the path of a light wave as it passes across the boundary separating two mediums. When light travels from one media with an index of refraction of n 1, into another media with an index of refraction of n , the incident ray of light and the refracted ray

2

of light are perpendicular to the boundary between the two materials, and lie in the same plane.

The angle of refracted light ray θ

2, is related to the angle of the incident light ray θ 1, by: n sin θ

= n sin θ 1

1 2

2

We can experimentally measure the index of refraction of a material by measuring the angles of the incident and refracted light rays, with the second media being air, which has an index of refraction of one ( ie: n2

= 1). In this way we can calculate n1 as: n2sinθ2 n =

1 sinθ1

II.

Materials and Methods

The materials used to execute the experiment consisted of white paper, a rhombus, a white light source and labels. A light source was placed on top of a piece of white paper. Labels were placed over the opening of the light source in order to create a thin projected light ray. An acrylic rhombus was placed in front of the light source so that the rays pass through the parallel sides.

The position of the parallel surfaces of the rhombus was marked and the incidence and refracted rays were recorded. The directions of the rays were indicated with arrows. The rhombus was removed and lines were drawn to connect the points locating where the rays entered and refracted from the rhombus. A line was drawn normal to the surface from the point where the ray entered the rhombus. The angles of incidence and refraction were measured with a compass; these angles were measured from the normal. These procedures were then repeated for five more incident angles.

Figure 1

Figure 1 represents the experimental set up.

III.

Angle of incidence( θ

)

Sin(

θ)

Results

Angle of refraction( θ′ )

Sin( θ′) n rhombu s

12°

.208

10°

.174

1.20

24°

.407

20°

.342

1.19

34°

.560

26°

.438

1.28

48°

.743

34°

.560

1.33

56°

.829

44°

.695

1.19

70°

.940

50°

.766

1.23

Avera ge index of refrac tion 1.24

Index of refrac tion (grap

h)

1.23

Figure 2-

Figure 2 Represents the angles of incidence in comparison to the angles of refraction. There is noticeable linear relationship between the two.

Figure 3-

Figure 3 represents the sine functions of the angles of incidence to the angles of refraction. The slope of the linear regression line gives the index of refraction, which is 1.23.

IV.

n

= n2sinθ2

1

sinθ1

Analysis

Lensmaker’s Equation:

Percent difference of focal lengths:

(12) n = 1.00sin

1

sin

(10) =1.20

=(1.241.5)/((1.24+1.5)/2)*100

(24) n = 1.00sin

1

sin

(20) =1.19

= 18.98%

(12) n = 1.00sin

1

sin

(10) =1.28

(12)

n

= 1.00sin

1

sin