Measuring the Index of Refraction

PHYS 205 SPRING 2007 Refraction

Examine the location and appearance of your finger as it is viewed through these shapes.

A. Describe the location of the finger portion viewed through this double concave lens. top view side view 1: finger on left side view 2: finger on right

side view 3: finger in middle

B. Describe the location of the finger portion viewed through this double convex lens. top view side view 1: finger on left side view 2: finger on right

side view 3: finger in middle

1 PHYS 205 SPRING 2007 I. Measuring the Index of Refraction: Gelatin Rectangle

 Place the gelatin rectangle on the grid paper. Trace around the rectangular tray.  Set your laser on the paper and shine it through the gelatin.  Mark the paper so that you can trace the path of the light through the gelatin container after removing the tray. Remove the tray and trace the path of the light.  Draw a normal at the location where the light entered the gelatin.  Measure the angles of incidence and refraction.  Use Snell’s Law to determine the index of refraction of the gelatin.  Repeat these steps at the location where the light leaves the gelatin and returns to the air.  Average the two indices of refraction and use to determine the speed of light through gelatin.

II. Measuring the Index of Refraction: Gelatin Semicircle

 Place the gelatin semicircle on the grid paper. Trace around the tray.  Set your laser on the paper and shine it through the gelatin, straight toward the plane side of the semicircle on the left side of the middle. Mark the paper so that you can trace the path of the light through the gelatin container after removing the tray.  Set your laser on the paper and shine it through the gelatin, this time straight toward the plane side of the semicircle on the right side of the middle. Remove the tray and trace the paths of the light.  Draw normals at the locations where the light exited the gelatin.  Measure the angles of incidence and refraction for both paths of light.  Use Snell’s Law to determine the index of refraction of the gelatin.  Average the two indices of refraction and use to determine the speed of light through gelatin.

III. Measuring the Index of Refraction: Water Semicircle

 Place the semicircle filled with water on the grid paper. Trace around the tray.  Put a small amount of coffee creamer in the water to make it cloudy.  Set your laser on the paper and shine it through the water, straight toward the plane side of the semicircle on the left side of the middle.  Mark the paper so that you can trace the path of the light through the water container after removing the tray.  Set your laser on the paper and shine it through the water, this time straight toward the plane side of the semicircle on the right side of the middle. Remove the tray and trace the path of the light.  Draw normals at the locations where the light exited the water.  Measure the angles of incidence and refraction for both paths of light.  Use Snell’s Law to determine the index of refraction of the water.  Average the two indices of refraction and use it to determine the speed of light through water.

2 PHYS 205 SPRING 2007 IV. Measuring the Critical Angle: Gelatin

 Place the gelatin semicircle on the grid paper. Trace around the tray.  Set your laser on the paper and shine it into the gelatin, toward the curved side of the semicircle.  Continue changing the angle of the incident laser beam until you notice total internal reflection within the gelatin.  Mark the paper so that you can trace the path of the light through the gelatin container after removing the tray.  Draw a normal at the location where the light experienced total internal reflection within the gelatin.  Measure the angle of incidence at the point of total internal reflection.  Use this value to determine the index of refraction of the gelatin.  Compare this value of the index of refraction with the values determined in parts I and II.

V. Measuring the Critical Angle: Water

 Place the water semicircle on the grid paper. Trace around the tray. Add coffee creamer until you can see the laser beam in the water. It only takes a little!  Set your laser on the paper and shine it into the water, toward the curved side of the semicircle.  Continue changing the angle of the incident laser beam until you notice total internal reflection within the water.  Mark the paper so that you can trace the path of the light through the water container after removing the tray.  Draw a normal at the location where the light experienced total internal reflection within the water.  Measure the angle of incidence at the point of total internal reflection.  Use this value to determine the index of refraction of the water.  Compare this value of the index of refraction with the values determined in part III.

3 PHYS 205 SPRING 2007