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Investigation 2 – PreLab









Physicists have created blue LEDs (light-emitting diodes) that have made today’s flat-panel, full-color computer monitors and TV screens possible. The technology also is being incorporated into water purifiers, which use ultraviolet light to kill bacteria and viruses in water.


This Investigation is designed to help you to answer the following Focus Question:

  • How does light wave interact with objects that reflect light? 

Note: This question is located in your SDR at the beginning and end of the Investigation.



As a class, read the Background(s) in the Investigation. When finished, discuss the following concepts as a class:

  • The Law of Reflection states that the angle at which light hits an object is equal to the angle at which light is reflected from the object.
  • The angle at which light hits an object is called the angle of incidence.
  • The angle at which light is reflected off of an object is called the angle of reflection.
  • The Law of Reflection states that the angle of incidence is equal to the angle of reflection.



The following list includes Key Terms that are introduced in the Investigation Background(s). They should be used, as appropriate, by teachers and students during everyday classroom discourse.

  • reflection
  • Law of Reflection
  • angle of incidence
  • angle of reflection

Note: Definitions of these terms can be found on the Introduction page to the CELL.

Note: Additional words may be bolded within the Background(s). These words are not Key Terms and are strictly emphasized for exposure at this time.


  • When studying reflection, it is useful to describe the events of reflection in terms of how light first interacts with a substance and how light is reflected off of a substance. Scientists give the light in each of these two steps different names, incident light, and reflective light.
    • Incident light is light from a source that interacts with the substance.
    • Reflected light is the light that is bounced off of the surface. It is this reflected light that enters our eyes and allows us to see the object.
  • Scientists characterize the way in which the incident and reflected light interact with a substance by describing the angles at which each comes in contact with the substance. These descriptions include the angle of incidence and the angle of reflection.
  • Play the video below. Remember to follow along with your SDR and make any notes that you think might be helpful in the lab.
  • After the video, divide into your lab groups to discuss strategy for the lab. For example, you may assign certain group members to perform specific functions during the lab.

Note: The purpose of the video is to allow you to anticipate the laboratory experience you will soon encounter. You should leave this PreLab session with a firm idea of what to expect and how to perform in the lab.

Note: Homework is posted below the video.


You should review the Investigation and video in preparation for the Lab.