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Reflection and Refraction

Objective: To explore the effects of different angles and materials on reflection and refraction using PhET simulations.

Methods

In this lab, we will use a PhET simulation to experiment with the behavior of light when interacting with various materials. We will begin at this site:

https://phet.colorado.edu/sims/html/bending-light/latest/bending-light_en.html

Once there, there are three options: Intro, Prisms, and More Tools. We will use the first two in this lab.

Procedure

1- Go to the Intro tab. Spend a few minutes playing with the various settings until you develop a feel for how the program works, then click the circular arrow in the lower right-hand side of the page to reset the screen to the default values. Place the protractor at the point where the light will intersect the surface. Use Snell's Law and the law of reflection to predict the following for an incident angle of 30 degrees.

Angle of reflection:

__________________________________________________________________ Angle of refraction:

_________________________________________________________________

2- Now turn on the light source and measure these angles with the protractor to the nearest degree.

Angle of reflection: __________________________________________________________________Angle of refraction: __________________________________________________________________

3- Now repeat this process for an incident angle of 80 degrees. Begin by predicting the reflected and refracted angles.

Angle of reflection:

_______________________________________________________________

Angle of refraction: _______________________________________________________________

4- Now move the light source to this position and measure these angles with the protractor to the nearest degree.

Angle of reflection: __________________________________________________________________

Angle of refraction: __________________________________________________________________

5- Return the light source to the 30 degree position, then adjust the index of refraction of the top half of the screen to be that of water.

6- What happens to the light ray in this case?

7- Now we will leave the top half of the screen as water, but make the bottom half air. Do not adjust the settings yet. Begin by predicting the reflected and refracted angles for the light ray at 30 degrees.

Angle of reflection: _______________________________________________________________

Angle of refraction: _______________________________________________________________

8- Now change the settings and measure these angles with the protractor to the nearest degree.

Angle of reflection: __________________________________________________________________

Angle of refraction: __________________________________________________________________

9- Now predict the reflected and refracted angles for the light ray at 80 degrees.

Angle of reflection: _______________________________________________________________

Angle of refraction: _______________________________________________________________

10- Now change the settings and measure these angles with the protractor to the nearest degree.

Angle of reflection: __________________________________________________________________

Angle of refraction: __________________________________________________________________

11- Find the critical angle for this situation, then adjust the angle of the light source to see if this is the case.

Predicted critical angle: _________________________________________________________________

Measured critical angle: _________________________________________________________________

12- Now go to the Prisms page. Spend a few minutes familiarizing yourself with the site, then when you are ready click the circular arrow to reset the page to the default conditions. Select the Semicircular lens and place it a few centimeters from the light source with the circular side facing the lens. Select the light source option with multiple lines, then turn on the light source.

1. Is this lens converging or diverging?

1. What happens to the light as you rotate the lens a few degrees?

1. Does it make any difference if the lens is reversed and the flat side faces the light?

13- Reset the page and select the hollowed out lens (at the far right). Place it in the same position as you did the semicircular lens, then turn on the light.

1. Is this lens converging or diverging?

1. What happens to the light as you rotate the lens a few degrees?

1. Does it make any difference if the lens is reversed and the flat side faces the light?

14- Reset the page and select the triangular prism. Place it in the same position as you did the other lenses, then turn on the light.

1. Is the prism converging or diverging?

1. What happens to the light as you rotate the prism a few degrees?

1. Describe the differences between the light's behavior with the prism and with the other lenses.

15- Finally, change the light setting to the white light. Observe the light's behavior as you rotate the prism. Look for a position with noticeable dispersion between colors. Explain why this happens in the space below.

Link: https://phet.colorado.edu/sims/html/bending-light/latest/bending-light_en.html