Instruction ManualManual No. 012-08690A

Solar ConstantModel No. TD-8497

Solar Constant Model No. TD-8497

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Table of Contents

Equipment List........................................................... 3

Introduction ............................................................. 4

Setup Procedure ........................................................ 4

Setup Options with ScienceWorkshop Interfaces .................... 5

Setup Options with PASPORT Interfaces ............................. 5

Experiment Tips ......................................................... 5

Suggested Experiment .................................................. 6

Teacher’s Notes......................................................... 8

Sample Data/Results.................................................... 9

Appendix A: Technical Support ....................................... 10

Appendix B: Copyright and Warranty Information .................. 10

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Model No. TD-8497 Solar Constant

Solar ConstantModel No. TD-8497

Equipment List

1 2 3 4

5

6

Included Equipment ReplacementModel Number*

1. Cylinder, aluminum, black, 1 inch 648-08684

2. Cylinder, aluminum, black, 0.75 inch 648-08686

3. Cylinder, brass, black, 0.75 inch 648-08688

4. Cylinder, aluminum, polished, 0.75 inch 648-08687

5. Cylinder, aluminum, white, 0.75 inch 648-08685

6. Mounting bracket with rod clamp 003-08691

*Use Replacement Model Numbers to expedite replacement orders.

Additional Equipment Required (for use with PASPORT) ReplacementModel Number*

Any PASPORT computer interface (PASPORT™ or ScienceWorkshop®) See PASCO catalog.

Quad Temperature Sensor (1) or Temperature Sensors PS-2143(1) orPS-2125(3) or PS-

2146(3)

Stainless Steel Temperature Probes (3) PS-2153 or CI-6605

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Solar Constant Model No. TD-8497

Introduction

The Solar Constant Set is used for discovering the rate at which radiant energy is received from the sun. Using the included bracket and a standard ring stand, these cylinders can be used to discover the solar constant or to simply compare the energy transfer to various cylinders.

In a typical experiment, the cylinders are each placed on a temperature probe and secured in a mounting bracket. The cylinders are taken outside and positioned such that each cylinder is perpendicular to the sun’s light rays. Using a fourth temperature probe (such as our Fast Response Temperature Probe (PS-2135), the ambient temperature can be measured throughout the entire experiment. The student typically collects temperature vs. time data for approximately one-half hour.

Setup Procedure

1. Insert a rod into a rod stand. Slide the rod clamp on the mounting bracket over the rod, and tighten the rod clamp.

2. With the big knob, set the angle so that the temperature probe points directly at the sun.

Note: The cylinders are designed to only fit the new stainless steel temperature probes (PS-2153 and CI-6605). The PS-2153 probe can be used with either a PASPORT Temperature Sensor (PS-2125), Pressure/ Temp. Sensor (PS-2146), Quad Temp. Sensor (PS-2143), or the CI-thermistor Sensor (CI-6527A). The CI-6605 Stainless Steel Temperature Probe plugs directly into a CI-interface.

3. Insert each probe through the hole in the bracket hole and tighten with a thumbscrew. Place a 1.5-in.

Figure 1: Setup with cylinders on temperature probes

piece of blue tubing over the bottom third of the probe to protect the probe. Blue tubing isprovided with both the Stainless Steel Temperature Probe and the Solar Constant Set).

Note: When securing the probe in the plastic holder, make sure that the thumb screw seats over the tubing, not directly on the stainless steel probe. Do not overtighten the screw, or you may collapse the probe.

4. Use the holes in the cylinders to fit the cylinders on the tip of the probes. You can position the cylinders either horizontally or vertically on the probe.

5. Connect each of the probes to a temperature sensor. (Note: The Quad Temp. Sensor (PS-2143) accommodates all four probes.)

6. Connect one or more temperature sensor(s) to either a PASPORT or ScienceWorkshopcomputer interface. (See the interface setup options on the this page.)

7. Open DataStudio. To begin collecting data, click the Start button.

Setup Options with ScienceWorkshop Interfaces

Interfaces - You can datalog with a 500 or 750 ScienceWorkshop interface in real time. With aScienceWorkshop interface, you can use up to three sensor ports.

Sensors and probes - Use the CI-Thermistor Sensor (CI-6527A), and either the PS-2153Stainless Steel Temperature Probe or the CI-6605 Stainless Steel Temperature Probe.

Setup Options with PASPORT Interfaces

Interfaces - Data log with any of the following: a) an Xplorer, b) laptop computer with USBlink or c) PowerLink with a laptop computer or a palm handheld device.

Sensors and probes - You can use either a single Quad Temperature Sensor (PS-2143) or three PS-2125 Temperature Sensors. A Quad Temp sensor is recommended. With a single Quad Temperature Sensor, you can attach four temperature probes (three stainless steel probes for the temperature of the cylinders and one Fast Response Temperature Probe (PS-2135) to separately monitor the ambient temperature).

Experiment Tips

1. Place the cylinders and entire apparatus outdoors in direct sunlight. This experiment must be performed in direct sunlight. It can be performed in early morning and late afternoon, but of course, the values you record in the early morning will be much lower. If you are trying to find the true solar constant, you will record a better value if you perform the experiment in the middle of a clear day in summer.

2. Aim and align the stainless steel probes directly at the sun. The best way to check alignment is to look at the shadow the cylinder casts on the base. This is why the base is white. If the experiment lasts for more than 10 or 15 minutes, recheck the alignment to account for the motion of the sun.

3. Record the initial temperature of the cylinders before starting the experiment. If you are trying to measure the solar constant, start with the cylinders at least 5°C below outside ambient temperature. If you bring the cylinders from inside where it is cool, this might be enough. If not, cool the cylinders with ice or cold water, but make sure they are dry before starting. Don’t get water in the holes of the cylinders. It also helps to have a shade to cover the cylinders while you set up and check alignment. When all three cylinders are at about the same temperature (at least 5°C below ambient temperature), start recording and remove the shade.

Suggested Experiment: Finding the Solar Constant

Equipment Required:

Solar Constant Set (TD-8497) (3) Stainless Steel Temperature Probes(PS-2153 or CI-6605))

Temperature Sensors: (1) PS-2143 or(3) PS-2125 or (3) PS-2146 or (3) CI-6527A

Computer interface (PASPORT orScienceWorkshop)

DataStudio software Standard Thermometer or Fast ResponseTemperature Probe (PS-2135)

Theory:

Q=mc∆T (1),

where Q=Thermal Energy added to the cylinder,

m=mass of the cylinder,

c=specific heat of the cylinder,

∆T=change in cylinder temperature

I Q ⁄ t= ----------

A(2),

where I=intensity of sunlight (Solar Constant), A=cross-sectional area of the cylinder (area of the shadow), and t=time.

Combining equations (1) and (2) yields

mc ∆

----T--- t

I = ---------------------

A

(3),

where ∆T ⁄ t is the cylinder’s rate of temperature change and also the slope of the ∆ T vs. tgraph.

Procedure

1. Follow the “Setup Procedure” on pages 4-5. Place the white, silver, and small aluminum (lighter weight), black cylinder each on a separate stainless steel temp. probe. If using the Quad Temperature Sensor, use a fourth temperature probe to measure ambient temperature. Otherwise, record the value of the outside ambient temperature with a standard thermometer. Make sure to start with the cylinders colder than ambient temperature (See “Experiment Tips” on page 5).

----

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

5 oC 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.

Figure 1-1: ExperimentSetup

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

(oC/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)].

mc ∆

----T

---

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

-------------t

--

A

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

where ( ∆ T/t) is the

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?

For Further Study:

1. Repeat the experiment with the three black cylinders.

2. Calculate the intensity, I, for all three cylinders. The heavier small black cylinder is made of brass. Did you record about the same intensity value for all three cylinders?

3. Look at the equilibrium temperature that each cylinder reaches. Why aren't the equilibria the same, in view of your answer from question (2)?

Teacher’s Notes

Shown below are typical heating rates of three aluminum cylinders with three different surfaces. Notice that both the heating rate and final temperature are largest for the black cylinder. The white cylinder clearly is the coolest at the final temperature. The slope on the graph is in degrees C/second, even though the axis is displayed in minutes. This data was taken in California during the summer around noon. The ambient temperature was measured with a Fast Response Temperature Probe, and thus the fluctuations there are real, due to very small air currents around the building. Also notice the small dip in all three temperatures at about 16 minutes, due to a small cloud that drifted by!

Heating Rates of Three Aluminum Cylinders with Different Surfaces

Sample Data

This graph shows cooling rates for the three aluminum cylinders with different surfaces. When the cylinders were moved inside to a cool room, the white cylinder emitted radiation almost as good as the black cylinder. The white cylinder cooled faster than the silver; this shows why white is the best overall color to keep cool!!!

Cooling rates of Aluminum CylindersMoved Indoors to a Cool Room

The following graph shows a comparison of heating rates for the three black cylinders, each of a different size and/or material. Note that the small cylinder heats up faster (because of a bigger surface to volume ratio, as expected) than the other cylinders, but the big cylinder has the highest final temperature. Why?

Heating Rates of Black Cylinders of Different Size and/or Material

Appendix A: Technical Support

For assistance with the TD-8497 Solar Constant Set or any other PASCO products, contactPASCO as follows:

Address: PASCO scientific

10101 Foothills Blvd.

Roseville, CA 95747-7100

Phone: (916) 786-3800

FAX: (916) 786-3292

Web: w w w .p a s c o.com

Email: te c hsupp@pasco. c om

Appendix B: Copyright and Warranty Information

Copyright Notice

The PASCO scientific 012-08690A Solar Constant Manual is copyrighted and all rights reserved. However, permission is granted to non-profit educational institutions for reproduction of any part of the 012-08690A Solar Constant Manual providing the reproductions are used only for their laboratories and are not sold for profit. Reproduction under any other circumstances, without the written consent of PASCO scientific, is prohibited.

Limited Warranty

For a description of the product warranty, see the PASCO catalog.