Download Reflection of a Ray of Light Introduction: Purpose

Investigation : Reflection of a Ray of Light
Introduction:
Light, from a source radiates in all directions. However, if we could place an opaque cover around the light source and poke a single hole in the cover, a single strand of light will emerge. We call this single strand of light a ray. Rays of light travel in straight lines. (rectilinear propagation)
A "beam" of light is a collection of parallel rays. This activity requires a single ray of light but the ray box used allows too many rays to pass through the slit. The said ray cannot even be called a beam because often, these rays aren't parallel. So, when doing this activity, realize that there is some uncertainty in your measures.
A "medium" refers to any change in the substance which interacts with the light. Some mediums are transparent meaning that _________________________, some mediums are translucent meaning that ________________________, and some mediums are opaque meaning that ________________________.
Provide an example for each of the following mediums.
transparent ______________, translucent _____________, opaque_______________
When a ray of light hits an opaque or translucent medium, the ray will likely be reflected. Sometimes only certain colours are reflected and sometimes only some of the light is relfected (partial reflection/refraction). Exceptions to this scenario would be black opaque objects and translucent mediums which are almost transparent.
The purpose of this activity is to determine the relationship between a ray hitting a perfect flat reflector (a plane mirror) and its reflected ray. Some key terms for this activity are as follows:
Incident Ray ­ the initial ray leaving from the light source
Point of Incidence ­ the exact location where the incident ray hits the mirror
Reflected Ray ­ the ray that bounces off the plane mirror
Normal ­ a line that is perpendicular to any surface. In this activity, the normal would be drawn as a dotted line at the point of incidence and perpendicular to the plane mirror
Angle of Incidence ­ the angle between the normal and incident ray
Angle of Reflection ­ the angle between the normal and the reflected ray Figure P3.1
Using a ray box to study the behaviour of light as it reflects off a plane mirror.
ray
box
plane mirror
incident ray
normal
point of incidence
Purpose: 1
Materials
ray box
ruler
protractor paper
plane mirror
pencil
Procedure
__ 1. Place a check mark (√) in the space provided as you complete each step.
__ 2. Draw slanted marks ( ) along the bottom of the line going acrosss the middle of the protractor paper. This symbolizes a reflecting surface. Label the line the reflecting surface.
__ 3. Find the midpoint of this line. Label it the point of incidence.
__ 4. Draw a dotted line perpendicular to the reflecting surface at the point of incidence. The line should go from the point of incidence past the edge of the protractor at the 90o mark. Label this line the normal. (place the label above the line)
__ 5. Using the protractor on the paper, draw, with a straight edge, 5 incident rays on either side of the normal such that the angle of incidence ­ the angle between the incident ray and the normal is at 0o, 15o, 30o, 45o, and 60o. Label these lines #1, #2,#3,#4,and #5. (The first line should be drawn at 90, the second line should be drawn at 75o or 105o, etc...)
__ 6. Place one direction arrow on each side of the incident rays near the number on the protractor to indicate the direction of the light rays.
__ 7. Stand a plane mirror vertically on the paper so that the reflecting surface (silver backside of the glass) is lined up with the reflecting surface line.
__ 8. Direct a single ray of light from the ray box to the mirror so that it follows the path of incident ray #1.
__ 9. Mark two points of the reflected ray (one near the mirror, one near the protractor's edge) on the paper. Remove the ray box and draw the reflected ray using the two dots indicating the path of the reflected ray. Label this reflected ray #1'. (Place the label above the protractor line.)
__ 10. Repeat steps 8 and 9 for incident rays #2 through #5. Label the reflected rays #2' through to #5'.
__ 11. Label this diagram Figure P3.2 and include an appropriate title.
__ 12. Remove the mirror from figure P3.2 and place it on the line near the bottom of the page.
__ 13. Replace the single slit of the ray box with a multiple slit (3 rays or 5 rays)
__ 14. Direct the multiple rays at the plane mirror such that the angle of incidence for each ray is around 30o.
__ 15. Mark the 3 incident rays using the two point method AND mark each of the reflect rays with a small "x" using the two point method again.
__ 16. Remove the light and use the mark paths of the rays to draw proper incident and reflect rays. Label each incident ray #1, #2, #3 and the corresponding reflected rays #1', #2', #3'.
__ 17. Label the diagram Figure P3.3 and include an appropriate title.
__ 18. Label the reflecting surface and use the appropriate marks to indicate the reflecting side of the mirror.
__ 19. Mark and label each point of incidence.
__ 20. Draw a normal for each point of reflection and label appropriately.
__ 21. Put away all the equipment.
__ 22. Prepare a table, Table P3.2 , with an appropriate title with the following headers: Ray #, Angle of Incidence, Angle of Reflection.
__ 23. Measure the angles of incidence and reflection for each of the 5 rays and record them in the table.
__ 24. Prepare a table, Table P3.3, with an appropriate title and the same headings as table P3.2
__ 25. Measure the angles of incidence and reflection for each of the rays in figure P3.3 and record in your table.
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Figure P3.2
Figure P3.3
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Analysis
The Law of Reflection states that the angle of incidence is equal to the angle of reflection. Result Summary Questions
1. Were the angles of incidence close to the angles of reflection? Close is not a mathematical term. Instead provide a range indicating the smallest difference and the largest difference.
2. When the values were different, were they all under, over, or did they vary?
Discussion Questions
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1. How certain were you of each measure? For example, if you wrote 16 , were you certain it was 16 or could your measure have been higher or lower.
2. Based on the certainty of your measures, do your results confirm the law of reflection? Explain
3. Did the law hold true for your results in Table P3.3?
Application Questions
1. Look up on the internet, the term diffuse reflection and regular reflection. a) Draw a diagram to illustrate the differences. b) Which type of reflection applies to this lab?
c) Does diffuse reflection defy the law of reflection? Explain. 4