Advance Physics

Prelab 8 (20 points)

You need a ruler and a protractor for this prelab. If you do not use them, you are not going to get any credit

Name Class Section

To get credit, always show your work and explain the number of significant digits you use

Refer to the photos on the first page of your handout and assume that the picture below is of the back of the tank shown there. The two colored lines represent two light rays aimed at the center of the tank.

You have filled the tank with water (refraction index n2=1.33) up to the black horizontal line. The top part of the tank contains air (refraction index n1=1.00). (2 points for the diagram)

Using your ruler and protractor, draw -according to the respective rules- the reflected and refracted rays for both incoming rays (the green one is 1 and the red one is 2) and write their angles.

1reflected =

2reflected2 =

1refracted =

2refracted =

Assume now that you mistakenly filled the tank up to the blue line in the figure below.

Using your ruler and protractor, draw the reflected and refracted rays for both incoming rays and read from the figure their angles (again, the green ray is 1 and the red one is 2).

Note: the point of incidence is now where each ray crosses the blue line. The angles from the normal lines in those two points are those calculated in the previous page. The angles you read from the figure (i.e. from the protractor in the figure) are not. These are the angles you have to write here below. (2 points for the diagram)

If you do not draw this diagram, any answer you give to the questions that follow will make no sense and you will not get any credit for them.

1reflected =

2reflected =

1refracted =

2refracted =

For each of the four angles calculate the changes in the angles of reflection and refraction:

1reflected - 1reflected =

2reflected - 2reflected =

1refracted - 1refracted =

2refracted - 2refracted =

Compare the changes for the reflection angles. Do you see a trend, depending on the incidence angle? Explain.

Compare the changes for the refraction angles. Do you see a trend, depending on the incidence angle? Explain.

Had you filled the tank below the central black line, instead than above, what do you think the errors (changes) in the measured reflection and refraction angles would have been?

The two most common causes of error are a) the tank is not horizontal, b) the tank is not filled to the line. Is it possible to distinguish between the two? YES NO How? (hint: what happens to the angles of reflection and refraction if the tank is tilted?)