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ENERGY TRANSFER: CONVECTION—LAB ACTIVITY
Energy Transfer: Convection
(Activity #13)
Purpose Determine how energy is transferred by convection in water.
Background Convection
Convection is the transfer of thermal energy by the movement of a
substance from one place to another. Convection takes place only in
liquids and gases.
For example, the lower
layers of the atmosphere
absorb infrared energy
emitted by the Earth’s
surface. The warmed
gas expands, rises, and
transfers thermal energy
to higher layers of the
atmosphere. Convection
in the atmosphere is
responsible for the
redistribution of thermal
energy from the
equatorial regions to the
polar regions as well as from the surface upward.
Convection is generally used to describe vertical motion. Advection is
sometimes used to describe horizontal motion, such as winds.
Convection also occurs in Earth’s oceans as
warmed water at the surface expands away and
cooler water from below wells up to the surface. In
water warmed at the bottom, the motion of the
warmed water is from the bottom toward the top.
As the surface water becomes cooler, it sinks
toward the bottom.
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ENERGY TRANSFER: CONVECTION—LAB ACTIVITY
Materials and
Equipment • Xplorer GLX • ice cubes (6)
Required • PASPORT Temperature Sensors (2) • string
• Large Tripod Base & Rod • plastic bag, approx. 1-L size
• Buret Clamp (2) • tape
• large straight-sided clear container • water
• heat lamp (or 150-W lamp) • white paper
• weight • lab coat (optional)
• food coloring
Safety Notes Remember, follow the directions for using the equipment.
Wear safety glasses and follow standard laboratory safety procedures.
Be careful when handling the heat lamp.
Keep water away from electrical outlets.
Pre-Lab How quickly will water temperatures change as a result of heating and
Question cooling due to a heat lamp shining on one part of the water and ice
added to another part of the water?
Procedure GLX Setup
1. Plug the PASPORT Temperature Sensors into the Xplorer
GLX.
2. Use the arrow keys ( ) to highlight the Flash folder,
select the Flash folder (press ), use the arrow keys to
highlight the file, and then open (press F1) the GLX
configuration file entitled
13 Convection CF
3. Open the Graph display (press , F1).
Note: The sensors have been configured to collect data once
every 2 seconds.
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ENERGY TRANSFER: CONVECTION—LAB ACTIVITY
Procedure, Equipment Setup
continued 1. Set up the tank of water. Fill the tank with room temperature
water to approximately 10 cm from the top.
2. Tape white
paper to one
side of the tank
to form a
backdrop so
you can more
easily view the
convection
currents in the
water.
3. Position the
heat lamp near one end of the tank.
4. Prepare the ice cubes by putting them in a plastic bag.
Squeeze as much air out of the bag as possible, and then
tie a piece of string around one end of the bag. Tie the other
end of the string to a weight.
5. Use the clamps and support rod to mount the two
Temperature Sensors at the middle of the tank so the tip of
one sensor is almost at the bottom of the water and the tip
of the other sensor is about 4 cm below the surface of the
water.
Record Data
The process is to turn on the heat lamp so it warms the water at
one end of the tank and then put the bag of ice cubes into the
water at the other end of the tank. The weight attached to the bag
of ice cubes will be an “anchor” to keep the bag in place. Use the
Temperature Sensors to measure the change in temperature of the
water near the bottom and near the top.
1. Press the Start/Stop ( ) key to begin recording data.
Turn on the heat lamp.
2. Carefully place the weighted bag of ice into the water at the
other end of the tank.
Note: The bag of ice will displace some of the water, so
watch the level of the water in the tank. Make sure that
none of the water spills out. The level of the water needs
to be within 5 cm of the top of the tank after you add the
ice, so put more room-temperature water into the tank if
needed.
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ENERGY TRANSFER: CONVECTION—LAB ACTIVITY
Procedure, 3. Wait 10 minutes for the temperature change to take effect, then
continued add 1 or 2 drops of food coloring into the water near the heat
lamp, and 1 or 2 drops of food coloring into the water near the
ice cubes. Note the time you added the food coloring.
4. Observe the motion of the food coloring to look for evidence of
convection. Record your observations. Be sure to include the
time relative to when you added the food coloring to the water of
each recorded observation.
5. After 20 minutes, press the Start/Stop key to stop recording
data.
6. Carefully remove the bag of ice cubes and turn off the heat
lamp. Continue to observe the motion of the food coloring.
Analyze
1. Examine your graph of temperature versus time to determine
how energy is transferred by convection.
(Hint: Compare the starting temperature for each sensor to the
final temperature. Which area of the water tank became colder?
Which area of the water tank became warmer?)
2. Make a sketch of your graphs. Be sure to label the x and y axes.
Add notes to your graph concerning the appearance of the food
coloring in the water at various points in time.
3. Save your GLX file (press , select Data Files, press F2).
Result: Your GLX file will be saved in the RAM folder.
Note: Your teacher may ask you to rename your file so you
can find it later. If so, use the following procedure:
1. Select the Files menu (press F4) and select Rename.
2. Key in the new name, and press the Save key (F2).
Analysis/ Analysis questions
Synthesis 1. What was the starting temperature for the water in both parts of
Questions the tank?
2. What was the final temperature of the water in the top part of the
tank?
3. What was the final temperature of the water in the bottom part of
the tank?
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ENERGY TRANSFER: CONVECTION—LAB ACTIVITY
Analysis/ Synthesis questions
Synthesis 1. Examine your graph of Temperature versus Time. How was
energy transferred by convection throughout the water tank?
Questions,
continued 2. Do your results support your prediction?
3. What evidence did you observe in addition to the temperature
that shows convection in the water?
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ENERGY TRANSFER: CONVECTION—LAB ACTIVITY
182 EXPLORATIONS IN EARTH & ENVIRONMENTAL SCIENCES
