REFRACTION OF LIGHT LAB – Due Thurs May 7th

Purpose: To observe the refraction of light as it passes from air into lucite and to experimentally determine theindex of refractionand critical angle for lucite.

Procedure:

PART A:

  1. Using a ruler, find the centre of the flat side of a piece of lucite. Put a mark with a permanent

marker at the centre point.

  1. Place the flat edge of the lucite along the horizontal 90oline of the polar graph paperso that thecenter mark of the lucite is on the 0o (horizontal) line – this is the normal. The curved portion of the lucite should be facing the top of the graph paper.

3. Direct a single ray of light from the ray box (use the single slit adapter) at the centre mark on the

flat surface of the lucite along the normal line. This is an angle of incidence (θi) of 0o.

4. Observe your angle of refraction where the refractedray leaves the curved surface and crosses the

angle markers at the top of the graph paper. Record this as theangle of refraction (θR)intable 1

(Air to Lucite)below.

5. Rotate the polar graph paper and lucite together so that the light from the ray box is incident at

5.0o and record the angle of refraction in table 1.(Remember: the angle of refraction is the

number ofdegrees from the normal).

6. Continue increasing the angle of incidence by increments of 5.0°, until you get to 80° measuring

the angle of refraction each time. Record your values in table 1 below.

ALWAYS AIM THE INCIDENT RAY AT THE CENTRE POINT OF THE LUCITE.

Table 1: The Angles of Incidence and Refraction of Light Passing from Air to Lucite

Angle of Incidence (θi) / Angle of Refraction (θR) / sinθi / sinθR
0 / 0
5
10
15
AVERAGE

Calculate the sinθiand sinθRfor each value and record them in table 1. Also calculate an average value for each of sinθiand sinθR.

Graph sinθivs sinθR (Graph 1 – Refraction from Air to Lucite)

Determine the index of refraction of lucite by calculating the slope of the line in the graph.

PART B:

  1. Flip the lucite over so that the curved surface is facing the bottom of the graph paper.
  2. Repeat steps 3 to 6 from PART A but record your values in table 2(Lucite to air).
  3. Make a note in table 2of the angle of incidence to the nearest 1° when the angle of refraction is 90o. This is the critical angle of incidence for light passing from lucite to air. Stop collecting data when you reach the critical angle.

Table 2: The Angles of Incidence and Refraction of Light Passing from Lucite to Air

Angle of Incidence (θi) / Angle of Refraction (θR) / sinθi / sinθR
0 / 0
5
10

Graph sinθRvs sinθi . (Graph 2 – Refraction from lucite to air)

Determine the index of refraction of lucite by calculating the slope of the line in the graph.

Inquiry Questions: Answer the following questions in complete sentences.

  1. When light moves from a medium of lower index of refraction to one with a higher index of

refraction (as in part A), does the light bend toward or away from the normal?How is the speed of light affected?

  1. When light moves from a medium of higher index of refraction to one with a lower index of

refraction (as in part B), does the light bend toward or away from the normal? How is the speed of light affected?

  1. What are the slopes of the lines ingraphs1 and 2 (these should also appear on your computer generated graphs in the form of an equation).
  1. Rearrangesnell’s law to show why the slope of the lines in graph 1 is equal to the index of refraction of lucite. (Use nair= 1.00 as your value for the index of refraction in AIR – do not substitute in values for the angles).
  1. Use snell’s law to calculate the index of refraction for lucite by using the average values of sinθi and sinθr from table 1.
  1. Compare your experimentally determined values from questions 3 and 5 for the refractive index of lucite to the actualvalue(you will have to research and citethe actual value from the internet).
  1. a) What did you experimentally determine the critical angle (θc) to be when light is refracted from lucite to air (PART B)?

b) Calculate the critical angle of light passing from lucite to air using the actual value(from Q. 6) for the index of refraction for lucite.

REFER TO THE BLUE LAB REPORT GUIDELINES SHEET YOU RECEIVED IN THE LAST UNIT

Extra notes for this particular lab:

Hypothesis – You don’t need one!

Procedure – Split this into Parts A and B, include a diagram for each part showing the light hitting the lucite. You may choose to draw the diagram. You do not need to include instructions for calculations or graphing.

Results - 2observationtables followed by 2 graphs–computer generatedwith lines of best fit and equations displayed.

Inquiry -Use complete sentences and show all calculations (for questions 4, 5 & 7).

Conclusion – Make sure you compare your experimentally determined results for n (there should be 3 total – 2 from the graphs and one from Q.5) and θc to the actual values. Discuss which of your n values you think is the most accurate. You will not need to reflect on your hypothesis.