Expriment 7: Introduction to Reflection and Refraction

9/22/2012

The purpose of the experiment is measure the incident angle and the refractive angle and find the relationship between them.

Equipment: Light box, semicircular plastic or glass prism, circular protractor, pasco optical kit or hardtl disk.

The angle of incidence for the light ray at the flat surface is theta1, the angle of refraction at the flat surface is theta2. When light ray leaves the plastic piece at the curved edge and goes in to the air, it has no refraction between the cured edge and air; just a straight light ray passing through it. This experiment is from lower density to higher density.

Set up the equipment shown as above and begin measure it. Let make theta1 begin from 5 degree to 70 degree.

Then we can collect the measurement and make a graph which is linear. We found that the slope is 0.6676. n1*sin(theta1)=n2*sin(theta2) We know that n1 is the index of air which is 1. so the 1/n2=sin(theta2)/sin(theta1)=0.667 then we can calculate the n2 which is index of glass is 1.49.

Then we change the the glass direction. And set up the equipment shown below.

 When the light ray through the first curved surface of the semicircular prism, the light ray doesn't have any changes. Because the angle of incidence is ever zero. When it strikes the flat surface, there is refractive angle. This experiment is from greater density to one of lower density.
Then we begin measure the angle of refraction and make a graph.

From the graph, we know we can complete all 10 trails, because when the incident angle is over 45degree. There has no refraction.

The slope of the graph is 1.46. n1*sin(theta1)=n2*sin(theta2) n2 is the index of air which is 1. So n1=sin(theta2)/sin(theta1) n1 is the index of glass which is 1.46.
Summary: Ok, now we have two slope of the graph which one of them is 0.667 and other is 1.46. Is it incorrect??? No for sure. Because they are different cases, one is from lower density to higher density; other is opposite. Although we used the same equation n1*sin(theta1)=n2*sin(theta2), but because the situation is different, so the n1, n2 will be changed. n2 is the index of glass from part one; n1 is the index of glass from part two. So the result we got 0.667 is closed to 1/1.46. Of course, we have some errors when we measure the refractive angle because the light is so wide not just like a small line.