This document describes an experiment to investigate refraction through a semicircular block with a different refractive index than air. Students are instructed to take angle of incidence and refraction measurements for light passing from air into the block. They will use these measurements to generate graphs of the sine of the angles and determine the refractive index. Comparing this value to the known refractive index allows them to verify Snell's law. The document also prompts students to apply their understanding by relating the results back to the original problem of why pencils appear separated in water and discussing other examples of refraction in daily life.

1. Worksheet 1st
Refraction in Difference Refractive Index
Name : ……………………………………………………………………………….
Class/absent : ……………………………………………………………………………….
Date : ……………………………………………………………………………….
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I. Problem
Why the pencils look separated each other?
II. Equipment
1. Semicircular block (n=1.485 - 1.755)
2. Light Box Ray
3. Protractor
4. Ruler
5. Sheet of Paper
III. Procedure
1. Make a data table with the following headings:
Angle of Incidence (θi), Angle of Refraction (θr), sin θi, and sin θr.
Incident Refraction
No sin θi sin θr
Angle(θi) Angle (θr)
1. … … … …
2. Draw a horizontal line across the sheet of paper so that the paper is divided into half.
3. Down the centre of the page, from top to bottom, draw a dashed line at right angles to the
horizontal line. This line is the normal line for the air-medium interface.
4. Using a protractor, draw lines on the top half of the page to represent the path of the
incident light in air for all of the angles shown in the diagram at right.
5. Place the semicircular block block of material on the page so that the straight side is
positionedon the horizontal line. Position the centre of the flat side of the block where the
normal line crosses the horizontal line (refer to the diagram).
6. Shine a single light ray from the ray box along the 10° line that you drew on the paper.
The ray should strike the flat side of the block of material at the centre and pass through
the block. Mark the paper at the point where the light ray exits the semicircular side of
the block. Label the incident light ray and the corresponding refracted light ray at the
point where it comes out through the semicircular side.

2. 7. Repeat step 6 for each of the angles of incidence shown in the diagram.
Protactor
θi
Incident Ray
Boundary
Semicircular Block
Reflacted Ray
θr
Normal
Pic: scheme of experiment
8. Remove the parallel and draw lines from the centre point where the rays entered the
block to the points where they exited. These lines are the paths of the refracted rays
9. Measure each angle of refraction and enter the data in your table.
10. Determine the values of the sinus of the angles of incidence and refraction, and enter the
data in your table.
IV. Analyze
1. What happens to the light when it passes from air into the refracting medium?
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2. As the angle of incidence increases, does the angle of refraction increase more rapidly
orless rapidly?
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3. Predict what will happen if the angle of incidence continues to increase. Is there a
maximum value for the angle of incidence?
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4. Plot a graph of θi (y axis) versus θr(x axis).
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5. Plot a graph of sin θi (y axis) versus sin θr (x axis).
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6. Compare the two graphs. How might such a comparison help scientists to
developempirical relationships?
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7. Determine the slope of the graph of sin θi versus sin θr. What does the slope of this line
represent?
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8. Compare the accepted value of the index of refraction of the material (semicircular block)
used in the investigation with the experimental value you just obtained.
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From the result analyze number 8 we get the terms of verification of Snell’s Law
mathematically.
9. Explain the physics meaning from the mathematic equation number 8.
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V. Apply and Extend
1. Related the Snell’s Law to the beginning problem.
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2. What if reverse from refracted from semicircular block to air? Anything happen
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3. As the angle of incidence increases, does the angle of refraction increase more rapidly or
less rapidly?
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4. What the factor of refraction?
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5. Give and explain based on Snell’s Law an example of refraction in daily life!
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