Lesson Plans: Why is it Hotter at the Equator?
Objective
The objective of this activity is to investigate the different heating effects of sunlight.
Materials
Each student or group of students will need the following:
- 3 identical Celsius thermometers (glass or metal backed)
- Reflector lamp with clamp and 60-watt light
- Ring stand with iron ring
- Utility clamp
- Black construction paper (one sheet per group of students)
- Stapler
- Several books to prop thermometers
- Metric ruler
- Scissors
- Graph paper
- Small ruler
- Pencil
Important Points to Understand
- Slanted light does not heat objects as quickly as direct light.
- Because the earth is nearly round, the equator receives direct light, and the poles receive slanted light, with a gradation in between.
- Due to the differential heating of the earth's surface, it is always warmer at the equator than at the poles.
Preparation
Be sure that all materials are either centrally located or already distributed to student groups. The teacher may do as much or as little preparation of materials (setting up lamps, covering thermometers) as is desired. The more preparation done ahead of time, the less time will be required for the activity, but the need for students to learn to use laboratory equipment should be considered. Use alcohol-filled thermometers for this activity. Urge students to use caution to avoid breaking the fragile thermometers and burning themselves on the lamp. Having a globe on hand may aid your discussion.
Procedure
- Use black construction paper to make a cover for the bulb of each thermometer as shown in Figure A. Cut a strip of black construction paper 5 centimeters x 10 centimeters. Fold the paper and staple four times. Insert the thermometer. Make three covers.
- Prop the thermometers as shown in Figure B. One thermometer should be vertical (A), one slanted at about a 45-degree angle (B), and one horizontal (C). Make sure you can easily read the scales without touching them during the experiment.
- Attach the lamp to a ring stand, being sure it will not move during your experiment. Adjust the lamp on the stand so that the light globe is centred 10 centimeters above the bulbs of the thermometers.
- Before turning on the lamp, record the temperature of all three thermometers in the table under the "0 minutes," column.
- Turn on the lamp and record temperatures for each thermometer every 3 minutes for 15 minutes. Do not move the thermometers when reading the temperatures. Record all temperatures in the table.
- Using the graph paper, make a graph of temperature versus time for each thermometer. To make comparison easier, plot the results for all three on the same graph paper, with different lines (solid versus dashed) to show the results from each thermometer.
Questions
- Which thermometer showed the greatest temperature increase? Why?
- Which thermometer(s) best represents the way sunlight strikes the equator? the poles? What parts of the globe would the third thermometer represent?
- Using what you learned in this activity, how can you explain the fact that the equator is always hotter than the poles?
- If you were given a data table that listed the average yearly temperatures for cities as you go away from the equator, do you think you would see a trend in the temperatures? If so, what should this trend be and why would it exist?
