Homework answers / question archive / Part A: Plane Mirror You can see someone else (or yourself) in a mirror when a light ray that leaves them reflects off the mirror and enters your eyes

Part A: Plane Mirror You can see someone else (or yourself) in a mirror when a light ray that leaves them reflects off the mirror and enters your eyes

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Part A: Plane Mirror
You can see someone else (or yourself) in a mirror when a light ray that leaves them reflects off the mirror and enters your eyes. Another way to describe this is to say that you can see someone in a mirror when there is a sighting line that goes straight from your eyes through the mirror to their image in the mirror.

1. Go to https://www.physicsclassroom.com/Physics-Interactives/Reflection-and-Mirrors/Who-Can-See-Who/Who-Can-See-Who-Interactive. Click on the arrows in the upper left-hand corner of the interactive, so that it fills the screen. Then select each student and click on all the students they can see in the mirror (including themselves!). When you have completed each student, a star will appear by their name on the main screen. Include a screenshot of the finished game in your lab report, showing stars next to each name.

Part B: Spherical Mirror
The ray-tracing practice pages from your lecture notes (which are also excellent summaries for each type of spherical mirror) will be very useful in completing this activity!

2. Go to https://www.physicsclassroom.com/Physics-Interactives/Reflection-and-Mirrors/Name-That-Image/Name-That-Image-Interactive . Click on the arrows in the upper left-hand corner of theinteractive, so that it fills the screen, and follow the instructions. When you have completed the activity,a star will appear by each of the 10 object positions. Include a screenshot of the finished game in yourlab report, showing stars next to each object position.
 

Part C: Snell's Law (from Chapter 26)
3.Go to https://phet.colorado.edu/en/simulation/bending-light. Choose the 'Intro' simulation. Click thered button to turn on the light ray. Place the protractor so that it measures both the angle of incidenceand the angle of refraction at the same time. Adjust the light ray so that the angle of incidence is 60?.Use Snell's Law to calculate the expected angle of refraction for the light ray as it enters the water. Nowmeasure this angle. Does it match the value you calculated?

4. Repeat the same calculation and measurement after changing the lower material to glass.
 

5. Now use Snell's law to solve for the index of refraction of both mystery materials A and B.
 

6. In following Snell's law as it goes from one medium into another, light does something else very interesting.
It always follows the particular path from one point to another that takes the least amount of time. This is
known as Fermat's Principle of Least Time. Go tohttps://www.physicsclassroom.com/PhysicsClassroom/media/interactive/LeastTimePrinciple2/index.html.
By precisely adjusting the point at which the lifeguard enters the water, find the path that takes the lifeguard
to the swimmer in the least amount of time. When you have found this point, click on 'protractor', and carefully
center the protractor on the target so that you can measure the angle of incidence and angle of refraction for
the lifeguard entering the water. The protractor in this simulation can be rotated, so make sure it's oriented
correctly. Verify that Snell's Law is obeyed by these angles. You will need to calculate the
"index of refraction" for both the sand and the water using the lifeguard's speeds in those materials.

 

Part D: Total Internal Reflection (from Chapter 26)
 

7. Finally, go back to https://phet.colorado.edu/en/simulation/bending-light. Choose the 'Intro' simulation
again. Adjust the index of refraction of the top material to 1.60, and the bottom material to 1.00. Move
the light source around and watch as the angle of incidence changes between 0?and 90?. Recall that
the critical angle is that point where total internal reflection begins. Carefully measure that angle. Now
use the appropriate formula to calculate the critical angle for light traveling between these two substances,
and verify that it matches your measurement.
 

8. Look up the index of refraction of diamond in your textbook. Calculate the critical angle for light traveling
from diamond to air. Use the value of this angle to explain why diamonds are so much more "sparkly" than
other materials.