PASCO TD-8497 Solar Constant User Manual

Page 8

Model No. TD-8497

Solar Constant

2. Place the cylinders in direct sunlight, check their

alignment, and start recording. To obtain the solar
constant, you only need to heat the cylinders to about

C above ambient temperature. To see the effect the

different surfaces have on the solar constant, allow the
temperatures to come to equilibrium.

3. To see the effect the different surfaces have on radiant

cooling after equilibrium is reached, shade the
cylinders, (or move them indoors) while still
recording. Continue recording until the temperatures
come to a new equilibrium.

Calculations

1. Look at the data for the black cylinder. Using DataStudio, do a linear fit for this data, but

highlight only the area near outside ambient temperature. (To do a linear fit, click the Curve
Fit button on the Graph display. From the menu of fit options, select “Linear Fit.”) Record
the slope of this line. At this point, the heating or cooling effect of the surrounding air is

eliminated, and the temperature increase is only due to the sun. The slope is the rate (

C/sec)

that the temperature is increasing.

2. Measure the mass (m) and the cross sectional area (A) of the black cylinder. Note that this

area is not the surface area, but the projected area of the shadow [A=(Length) x
(Diameter)].

3. Calculate the intensity of the sunlight (solar constant),

where ( T/t) is the

slope from your graph, and c is the specific heat of aluminum.

Questions:

1. Calculate the intensity, I, for the white and silver cylinders. Why are they so much less?

Where does the energy go?

2. Which cylinder initially heats up faster, the white or silver cylinder? Look at the values

for the intensity (I) from question (1).

3. If you left the cylinders in the sun long enough to come to equilibrium, you should see that

the white cylinder is the coolest at equilibrium. Does this make sense based on how you
answered question (2)?

4. Look at the cooling curves at the point when the cylinders were removed from the

sunlight. Which color cylinder has the steepest cooling curve? Which color cylinder
radiates energy better?

Figure 1-1: Experiment
Setup

mc ∆

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