Kristen Robinson

EMAT 4680

7 November 2000

Lab Write-up 4

Title: Intense Light

Team Members: Megan and Lee

Materials: CBL with light monitor, graphing calculator, flashlight, 2 meter sticks, box at least 1 meter long, masking tape

Procedure:

1. Tape one tape measure to the table.

2. Tape the CBL light monitor to the 100 cm end of the second meter stick.

3. Set up the CBL and the graphing calculator so the data from the CBL is sent to the graphing calculator.

4. Place the second tape measure next to the first tape measure, making sure the 0 on the first and the 100 on the second are right next to each other.

5. Place the flashlight so the lit end is at the 0 cm mark on the first tape measure, facing the CBL.

6. Place the box over the set up so that the only light under the box is the lit flashlight.

7. Move the tape measure with the CBL on it 10 cm away from the flashlight. Record

the distance in cm of the CBL monitor to the flashlight. Record the intensity value from the CBL (in lumens).

8. Repeat step 7, moving the CBL tape measure 10 cm each repetition until the CBL no longer lies under the box.

Data Set:

Independent Variable	Dependent Variable
Distance from Source (cm)	Intensity (lumens)
10	0.893
20	0.89
30	0.885
40	0.875
50	0.866
60	0.857
70	0.843
80	0.7

Scatter Plot:

Analysis of Data:

The best fit function to model the experimental data is y = (-7E-11)x^6 + (2E-8)x^5 - (1E-6)x^4 + (6E-5)x^3 - .0015x^2 + .0171x + .8211. This is a polynomial function of degree 6. This is the same as a square of a cubic function or the cube of a quadratic function. The y-intercept of the graph is at y = .8211. Therefore, when the CBL is 0 cm from the light source, the intensity of the light should be .8211 lumens. The domain of the function should be limited to x >= 0. This is because the CBL cannot be a negative distance from the light source. The graph of the function reflects that the intensity of the light source on the CBL decreases as the distance between the light source and the CBL increases. This is a logical conclusion.

Conclusions & Extensions/Predictions:

CBL experiments can be very time-consuming in the high school classroom. Students may not know how to use the CBL, especially in conjunction with the graphing calculator. Therefore, the teacher must take time away from the experiment in order to teach the students how to use the CBL. However, this lesson would only need to be taught once. The error in this lab primarily has to do with the amount of outside light blocked by the box. It is virtually impossible for the box to block ALL outside light in the experiment. Therefore, error in light intensity can occur.