Light Up the Planet
There is no doubt you’ve been hearing a lot of talk these days
about global warming and climate change. But what is causing
the temperature of the Earth to rise? This edition of THE LAB
will help you explore how sunlight influences rising
temperature, and how different colours affect energy
absorption.
What you’ll need:
• thermometer
• a few cardboard boxes with open lids (such as pizza boxes
without lids)
• coloured construction paper (white, black, yellow, red, blue)
• plastic Saran wrap
• tape
• a sunny location in which you can leave the box
What to do:
1. Tape the thermometer to the bottom of the cardboard box,
taking care not to cover the bulb with the tape.
2.Cover the bottom of the box (not including the thermometer)
with black construction paper and then cover the top of the
box with plastic Saran wrap.
3. Place the box in the shade for 10 minutes record the
temperature.
4. Next, place the box in direct sunlight. Every 5 minutes, record
the temperature. How is it changing?
5. Repeat these steps but instead line the box with white
construction paper (if you have two thermometers and two
boxes, you can do both at the same time). How is the
temperature change in the the white box different than in
the black box?
6. Once again, repeat these steps with the other coloured
construction paper. Does the temperature change when you
use different colours of paper? By how much?
Note: if you can’t find direct sunlight, you can use a 100 watt
halogen light bulb (2 feet away from the box).
thermometer
cardboard
box
black paper
(or other colours)
What’s the science?
The darker an object is, the more light it absorbs. In contrast, a light or
bright object will reflect a lot of light.
Light is one form of energy, and when the dark paper absorbs incoming
light, it stores this as thermal energy and the temperature in the box rises.
The thermal energy will remain trapped inside the plastic-wrapped box
and you can measure the temperature change on the thermometer.
Now, think about the Earth and the so-called
Greenhouse Effect.
How is the Earth like the cardboard box?
The light areas of the Earth, such as the snowy North
and South Poles, reflect a lot of light, but more coloured
parts, such as the vast oceans, absorb the light and
warm up the Earth. The atmosphere helps trap the heat,
just like the plastic wrap trapped the heat in the
cardboard box. The trapped heat causes more snow
and ice to melt, providing less light surface for
reflecting light and more dark water for absorbing light.
Although this is not the only reason for global warming, this pattern of
melting snow does add to the overall warming of the Earth.