Lab Report
Introduction
The purpose of the experiment was to show how prism separates white light into its component colors and to show how different colors are refracted at different angles through a prism. It was hypothesized that violet color would be the most refracted because it had the lowest wavelength.
Materials
- Light source
- Trapezoid from Ray Optics Kit
- Blank White Paper
Procedure
The light source was placed in a ray box mode on a sheet of blank white paper and a single white ray was selected by turning the wheel. Trapezoid was positioned such that its acute angle side faced the light source. The trapezoid was rotated until the ray separated into colors and the angle (θ) of emerging ray was as large as possible. The color names and order was observed. The wheel was turned to select three primary colors. Without changing the position of light source, red, green and blue colors were selected by turning the wheel. The colors were made to pass through the trapezoid at the same point the white light passed.
Results
Colors observed
Red-at the bottom nearest to the emerging ray
Orange
Yellow
Green
Blue
Indigo
Violet-at the top far farthest from the emerging ray
Color refracted at the largest angle θ
Violet
Analysis
Snell law can be written as;
Ѵ1 /Ѵ2 = Sin θ2 / Sin θ2 = n1/n2
Discussion
The white light was separated into seven colors because of the refraction. White light is made up of seven colors with different wavelengths. Refraction occurs because each color travels at different speed in the acrylic medium. The most refracted color was violet while the least refracted was the red. Red has the lowest frequency while violet has the highest frequency. The color ray that emerged from three primary colors was a single white ray. This was in line with the principle of reversibility of light which states that light traces its own path. Consequently, the light cannot emerge as parallel rays.
Conclusion
The hypothesis was upheld because the red light was the least refracted.
Experiment 3
Introduction
The purpose of the experiment was to study how rays are reflected from different types of mirrors and to measure the focal length and determine the radius of curvature of concave mirror and convex mirror. It was hypothesized that the reflected ray from concave mirror and convex mirror would converge and diverge respectively.
Materials
- Light source
- Mirror from Ray Optics Kit
- Drawing compass
- Protractor
- Metric ruler
- White paper
- Trapezoid from Ray Optics Kit
- Blank White Paper
Procedure
Part 1: Plane Mirror
The light source was placed in a ray box mode on a blank sheet of white paper and a single ray was selected by turning the wheel. The mirror was placed on the paper with its flat surface positioned in the path of the incident ray at an angle that allowed both incident and reflected ray could to be observed. The surface of the mirror, incident and reflected rays were traced on the paper. The appropriate direction of the incoming and outgoing rays was indicated using arrows. The light source and mirror were removed from the paper and normal drawn on the surface. The angle of incidence and reflection were measured. The procedure was repeated with different angle of incidence and angle of reflection determined and recorded. Three primary color rays were selected by turning the wheel. The rays were shone on the plane of the mirror. The incident and reflected rays were traced. The name of the colors was indicated and the appropriate direction of incoming and outgoing rays indicated.
Part 2: Cylindrical Mirrors
Five parallel rays were selected by turning the wheel. The light was shone into concave mirror so that the rays were reflected back. The surface of the mirror, the incident ray and reflected ray were traced. The appropriated directions of incoming and outgoing ray were indicated. The point where the reflected rays met was marked. The focal length was measured. This was the length from center of concave mirror surface to the focal point. A circle that matches the curvature of the mirror was drawn using a compass. The radius of curvature was measured. The procedure was repeated for convex mirror. For convex mirror the focal point was located by extending the reflected rays behind the mirror surface.
Results
Analysis
According to the law of reflection;
Angle of incidence = Angle of refraction
θ i = θ r
The radius of curvature R is twice the focal length f
R = 2f
Discussion
The measured angles of incidences were equal to the corresponding angles of reflection. Thus, the law of reflection was observed. The reflected rays of the three colors were not reversed because the angle of incidence of each color was equal to the angle of reflection. The radius of curvature of a convex or concave mirror is twice the focal length. This relationship was not observed because of inaccurate determination of radius of curvature. Nonetheless, the determined radiuses of curvatures were closer to the predicted values. The focal point for plane mirror is undefined or infinity.
Conclusion
The reflection of light by plane and curved mirrors obeyed the law of reflection. The hypothesis was upheld because concave and convex mirrors produced converging rays and diverging rays respectively.
Experiment 4
Introduction
The purpose of the experiment was to determine the index of refraction of the acrylic trapezoid.
Materials
- Light Source
- Trapezoid from Ray Optics Kit
- Protractor
- White paper
Procedure
The light source was placed in a ray box mode on a sheet of white paper and single ray was selected by turning the wheel. The trapezoid was placed on whitepaper. It was positioned such that the incident ray passed through parallel side. The position of parallel surfaces of the trapezoid was marked and the incident and transmitted ray were traced. The appropriate directions of the incoming and outgoing rays were indicated with arrows. The trapezoid was removed and a line connecting the points where the rays entered and left the trapezoid was drawn. This line represented the ray that passed through the trapezoid. A normal to the surface was drawn at a point where the rays entered the trapezoid. The angle of incidence and angle of refraction were measured using a protractor. These angles were recorded. The procedure was repeated for different angle of incidence.
Results
Analysis
Snell law n1Sin θ1= n2 Sinθ2
Sin 61º / Sin 35º
1.52
Sin 52º / Sin 33º
1.45
Sin 82º / Sin 39º
1.57
Average = (1.52 + 1.45 + 1.57) ÷ 3
1.51
Percent difference = (0.01 / 1.5) X 100
1.5%
Discussion
The incident ray and the emergent ray were parallel. Consequently, the angle of the ray that left the trapezoid was equal to the angle of ray that entered the trapezoid. This was brought by the fact that the two surfaces were parallel.
Conclusion
The refractive index of the acrylic as determined by Snell’s law was closer to the accepted value of 1.5. Meaning, there were minimal errors.
Experiment 5
Introduction
The purpose of the experiment was to determine and confirm the critical angle at which total internal reflection occurs in acrylic using Snell’s law.
Materials
- Light source
- Trapezoid from Ray Optics Kit
- Protractor
- White paper
Procedure
The light source was placed in a ray box mode on a sheet of white paper and single ray selected by turning the wheel. The trapezoid was positioned in a way that the ray entered it at 1.5cm from the tip. The trapezoid was rotated until the emerging ray disappeared and the colors separated. The surface of the trapezoid was marked. The point where the ray was internally reflected was marked. The entrance point of the incident ray and exit point of the reflected ray were also marked. The trapezoid was removed and rays that was incident upon it and the reflected ray from the inside surface of the trapezoid were drawn. The angle between these rays was measured using the protractor. The critical angle was recorded.
Results
Critical angle θ = 39º
Analysis
Sin C = 1÷1.5
0.667
C = 41.81
Percent difference
[(41.81 – 39) ÷41.81] X 100
6.72%
Discussion
The brightness of internally reflected ray increased when the incident ray was changed from less than C towards C. On the other hand, the brightness decreased when the angle was changed from C to greater than C where C was the critical angle. The critical angle is greater for red light than violet light. Meaning, index of refraction would be greater if violet light was used.
Conclusion
Critical angle is an accurate method of determining the index of refraction of substances.
