Name ______

Energy Transfer by Radiation and Absorption

Introduction:

When the sun’s radiant energy strikes the Earth, the temperature of the surface tends to increase. Throughout our own experience you know that some surfaces warm faster than others. Materials that heat up quickly do so because they are efficient absorbers of radiant energy. The two variables that effect absorption rates are color and surface area. Radiation may also be released (re-radiated) from the surface of an object. The same variables mentioned above also effect the rate at which energy is released (emitted). In this investigation the absorption and re-radiation rates of two different aluminum cups will be investigated.

Objective:

You will be able to measure and explain the properties that would cause a surface to be an efficient absorber and radiator of radiant energy.

Vocabulary:

Absorption-

Radiation –

Re-radiation-

Rate–

Procedure: Assemble the apparatus by following the directions below:

  1. Arrange the black and silver (shiny) cups in front of the heat light at a distance of 20 cm from the light bulb. Keep the cups about 5 cm from each other.
  2. On the Data Table, record the temperature in degrees Celsius for each cup at Time 0.
  3. Turn on the lamp and read the thermometers at one minute intervals for 10 minutes. Record the data on the Data Table.(Heating)
  4. Turn off the lamp and read the thermometers at one minute intervals for 10 minutes (time 11-20). Record the data on the Data Table.(Cooling)
  5. Graph your data. You will have a total of 2 lines on your graph.
  6. Graph 1- Heating and cooling of black cup
  7. Graph 2- Heating and cooling of shiny cup

Data Table:

Table One: Temperature of Light and Dark Cups

TIME IN MINUTES / 0 / 1 / 2 / 3 / 4 / 5 / 6 / 7 / 8 / 9 / 10
Temperature of “Shiny/Light” cup
Temperature of “Dull/Dark” cup
TIME IN MINUTES / 11 / 12 / 13 / 14 / 15 / 16 / 17 / 18 / 19 / 20
Temperature of “Shiny/Light” cup
Temperature of “Dull/Dark” cup

Absorption and Re-Radiation Rates


Questions:

  1. Which container was exposed to the most radiation from the source?
  1. Which container absorbed the energy at the highest rate? Calculate the Rate of Absorption for first 10 minutes (from time 0 to 10).
  1. Which container re-radiated energy at the highest rate? Calculate the Rate of Re-Radiation for the last 10 minutes (from time 11 to 20).
  1. Reflection and Re-radiation are often confused. Can you explain the difference using examples observed in this experiment?
  1. What statements can you make about how color and surface area affect the rate of energy absorption?
  1. How can you tell by looking at the graph which container heated up and cooled down most rapidly? Consider what property of a graph indicates rate.
  1. Explain why a person in a hot climate would benefit from wearing white clothing.
  1. If the sun’s radiation is striking Ice and Soil in two different areas, how would the observations in this lab to the absorption and re-radiation rates in this real world example?

REGENTS QUESTIONS