Lab: The Reason for the Seasons

Introduction: We have learned that the reason we have seasons on Earth is that Earth is tilted on its axis of rotation 23.5 degrees. As Earth orbits the sun, different parts of the earth receive more direct, concentrated sunlight at different times of year. The purpose of this lab is to demonstrate how the angle of the sunlight affects its intensity.

Materials:

·  flashlight

·  graph paper

·  several textbooks

·  ruler

·  protractor

·  colored pencils (green, blue, purple, orange, brown)

Procedure:

Preparing the Light Source

1.  Make a stack of textbooks about 6 inches high on the lab table.

2.  Lay the flashlight on its side on top of the stack of books, lining up the edge of the flashlight so it is close to the edge of the stack. Use masking tape to tape the flashlight down so it can't roll around. (See Figure 1)

Preparing the Surface:

1.  Use the clear tape to attach a sheet of graph paper to another textbook. (Use an uncovered textbook, so the tape will come off easily when you are done.)

2.  Turn on the flashlight. (Please, do not waste the flashlight batteries!)

3.  Hold the book with attached graph paper vertically in front of the flashlight, as shown in Figure 1. Move the graph paper closer or farther away from the flashlight, until the light on the paper forms a medium-sized, sharp circle about 2–3 inches in diameter.

4.  Measure the distance from the edge of the graph paper to the flashlight and record this number as “starting distance” in your science journal. Make certain to keep the graph paper at this starting distance for all testing!

Fig. 1: Experimental set-up

Procedure:

1.  One person should hold the graph paper vertically (straight up and down) at the starting distance in front of the flashlight.

2.  Another person should use a green colored pencil to draw around the outline of the light on the graph paper. Just draw around the most intense circle of light.

3.  Observe the brightness of the light inside this outline and record your observations.

4.  Place the protractor next to the graph paper so that the 90 º mark is lined up with your vertical textbook. Now tilt the textbook with attached graph paper 10 º.

5.  Use a blue colored pencil to draw around the outline of the light on the graph paper. (Again, trace only the most intense area of light.)

6.  Observe the brightness of the light inside this outline, and record your observations and compare the brightness of the light at this angle to the previous outline.

7.  Repeat steps 4–6 for tilt angles of 20°, using a purple pencil, 30°, using an orange pencil, and 40°, using a brown pencil.

1.  Draw the data table in your Journal. Use a ruler!

2.  Count the approximate number of squares inside each light outline. Record your counts in the data table.

NOTE: For partial squares, estimate how much of the square is lit up; for example, if it looks

like one-fourth of the square is lit up, add 0.25. If it looks like half of the square is lit up, add 0.5,

and so forth. (Use decimals, not fractions!)

3.  Send someone from your group to record your data in the Table on the Smartboard. When we have all groups’ data, we will calculate averages and you will record them in your own data table.

Data Table: Number of Lighted Squares

Degree of tilt / 0°
(green) / 10°
(blue) / 20°
(purple) / 30°
(orange) / 40°
(brown)
Number of squares within the outline
Class Average Number of Squares within the outline.

Questions and Conclusions:

Answer these questions in your science journal in complete sentences that can be understood without knowing the questions. DO NOT copy down the questions! You may discuss the answers among your group members, but each person must write the answers in his or her OWN words!

1.  What was the independent variable in this experiment?

2.  What was the dependent variable in this experiment?

3.  Why did we have to always hold the graph paper at the same “starting distance”?

4.  What are some other constants in this experiment?

5.  How did the numbers of squares inside the outline change as the degree of tilt increased?

6.  How did the brightness or intensity of the light change as the degree of tilt increased? (Hint: if the same amount of light is being spread over a greater area, is each individual square receiving more or less light than when the light I more concentrated onto a smaller area?)

7.  Explain how this demonstration models the way the intensity of sunlight shining on Earth changes over the course of the year. Be detailed in your explanation.

8.  What degree of tilt produced light similar to what North America experiences in summer? Explain why.

9.  What degree of tilt would produce light similar to what N. America experiences in winter? Explain why.

10.  Summarize how the results of this experiment can be used to better understand the reason for seasons.

REASONS for SEASONS LAB -- Questions and Conclusions: Answer these questions in your science journal in complete sentences that can be understood without knowing the questions. DO NOT copy down the questions! You may discuss the answers among your group members, but each person must write the answers in his or her OWN words!

1.  What was the independent variable in this experiment?

2.  What was the dependent variable in this experiment?

3.  Why did we have to always hold the graph paper at the same “starting distance”?

4.  What are some other constants in this experiment?

5.  How did the numbers of squares inside the outline change as the degree of tilt increased?

6.  How did the brightness or intensity of the light change as the degree of tilt increased? (Hint: if the same amount of light is being spread over a greater area, is each individual square receiving more or less light than when the light is more concentrated onto a smaller area?)

7.  Explain how this demonstration models the way the intensity of sunlight shining on Earth changes over the course of the year. Be detailed in your explanation.

8.  What degree of tilt produced light similar to what North America experiences in summer? Explain why.

9.  What degree of tilt would produce light similar to what N. America experiences in winter? Explain why.

10.  Summarize how the results of this experiment can be used to better understand the reason for seasons.

REASONS for SEASONS LAB -- Questions and Conclusions: Answer these questions in your science journal in complete sentences that can be understood without knowing the questions. DO NOT copy down the questions! You may discuss the answers among your group members, but each person must write the answers in his or her OWN words!

1.  What was the independent variable in this experiment?

2.  What was the dependent variable in this experiment?

3.  Why did we have to always hold the graph paper at the same “starting distance”?

4.  What are some other constants in this experiment?

5.  How did the numbers of squares inside the outline change as the degree of tilt increased?

6.  How did the brightness or intensity of the light change as the degree of tilt increased? (Hint: if the same amount of light is being spread over a greater area, is each individual square receiving more or less light than when the light is more concentrated onto a smaller area?)

7.  Explain how this demonstration models the way the intensity of sunlight shining on Earth changes over the course of the year. Be detailed in your explanation.

8.  What degree of tilt produced light similar to what North America experiences in summer? Explain why.

9.  What degree of tilt would produce light similar to what N. America experiences in winter? Explain why.

10.  Summarize how the results of this experiment can be used to better understand the reason for seasons.