# How does the temperature of dry sand and water differ when they are exposed to radiation from the lamp? Suggest a reason why the sand and the water may heat differently?

Sketching Assignment – Global temperatures, Solar Radiation, Insolation and Albedo

1All answers must in red or underlined if you plan on using the Word file.

Insolation

Figure 2 demonstrates how insolation varies with latitude on the Earth. Each shaded box, A, B, and C represents a beam of solar radiation impinging on the Earth at different latitudes. Each beam on Figure 2 is 1.0 cm wide.

For each latitude, draw a chord connecting where the upper part of the beam intersects the Earth’s surface to where the lower part intersects the Earth’s surface. For clarity, it is best if you can do this in a color other than black. Using a cm scale, measure the length of each chord. For example, the chord length of beam A should be 1.0 cm. Enter your measurements in the table above.

The acute angle between the beam and the Earth’s surface is known as the angle of incidence.

Using a protractor, measure the angle of incidence between the chord and the centerline of each beam. For example, at the Equator (Beam A, latitude 0°), the angle of incidence is 90° whereas at the poles (latitude 90°), the angle of incidence is 0°. Enter your measurements in the table above.

The relative intensity is a measure of the amount of insolation that is available at a given latitude relative to that at the Equator. The larger the area upon which the beam is spread out, the lower the

A

B

C

60° N

30° N

S

U

N

Figure 2. Angle of incidence and relative insolation at 0°, 30°, and 60° latitudes.

Beam Latitude Angle of incidence

Beam

width

(cm)

Chord

Length

(cm)

Relative intensity

(%)

𝐵𝐵𝐵𝐵𝐵𝐵𝐵𝐵 𝑤𝑤𝑤𝑤𝑤𝑤𝑤𝑤ℎ

𝐶𝐶ℎ𝑜𝑜𝑜𝑜𝑤𝑤 𝑙𝑙𝐵𝐵𝑛𝑛𝑛𝑛𝑤𝑤ℎ × 100

A 0° 90° 1.0 1.0 100%

B 30° 1.0

C 60° 1.0

Sketching Assignment – Global temperatures, Solar Radiation, Insolation and Albedo 2 intensity.

The relative intensity is always less than or equal to 1 and is calculated from the following equation,

𝑅𝑅𝐵𝐵𝑙𝑙𝐵𝐵𝑤𝑤𝑤𝑤𝑅𝑅𝐵𝐵 𝐼𝐼𝑛𝑛𝑤𝑤𝐵𝐵𝑛𝑛𝐼𝐼𝑤𝑤𝑤𝑤𝐼𝐼 (%) = 𝐵𝐵𝐵𝐵𝐵𝐵𝐵𝐵 𝑤𝑤𝑤𝑤𝑤𝑤𝑤𝑤ℎ

𝐶𝐶ℎ𝑜𝑜𝑜𝑜𝑤𝑤 𝑤𝑤𝑤𝑤𝑤𝑤𝑤𝑤ℎ × 100

For example, at the Equator (Beam A), the chord is perpendicular to the beam and the same width (= 1.0 cm), so that the relative intensity of insolation at the equator is 100%.

Calculate the relative intensity for each beam and enter the results in the table.

Based on your results, how do the angle of incidence and relative insolation relate to latitude?

How do your conclusions in this theoretical experiment help explain your observations in the ApprenNet assignment?

Figure 2 compares the change in insolation on the December solstice (December 22 nd ), June Solstice

(June 21 st ) and the Equinoxes (March 21 st and September 23 rd ). At each of these times, indicate which region receives the greatest amount of insolation (circle one)

December solstice: Northern Hemisphere / Equator / Southern Hemisphere

Equinox: Northern Hemisphere / Equator / Southern Hemisphere

June solstice: Northern Hemisphere / Equator / Southern Hemisphere

Sketching Assignment – Global temperatures, Solar Radiation, Insolation and Albedo 3

Figure 1. Comparison of the variations in insolation on the Earth during the changes in the seasons. From, Reynolds, S and J.

Johnson, Exploring Earth Science. McGraw Hill, 2016

The seasons also effect the length of day (the time between sunrise and sunset). Based on your observations of Figure 2, indicate when each region has the longest day (circle 1)

Northern Hemisphere: December Solstice / The Equinoxes / June Solstice

Equatorial Region: December Solstice / The Equinoxes / June Solstice

Southern Hemisphere: December Solstice / The Equinoxes / June Solstice

Albedo

Place equal amounts of black sand and white sand into the beakers provided. Place thermometers in the sand of each so that the bulb is about ¾ inch beneath the surface of the sand. Place the two beakers at the equal distance away from the lamp provided (lamp should be off). Note the temperature in both sets of sand and enter in the table

Switch on the lamp and then note the temperature in each beaker every minute (use the stop watch function on your cell phone) and enter the temperature into the table. After 10 minutes switch off the lamp. Plot the temperature vs. time on the chart provided. Use a different colors to represent the black and white sands.

See the file named “Albedo Sand Results” in the assignment dropbox for the temperature values.

Table 1. Temperature Data for Albedo Experiment

Starting

Temp

(°C)

1

min

(°C)

2

min

(°C)

3

min

(°C)

4

min

(°C)

5

min

(°C)

6

min

(°C)

7

min

(°C)

8

min

(°C)

9

min

(°C)

10

min

(°C)

Black

Sand

White

Sand

Sketching Assignment – Global temperatures, Solar Radiation, Insolation and Albedo 4

Calculate the rate of heating for each sand (= change in temperature/time light was on).

Black Sand: ________________ White Sand: _________________

Explain the result of the albedo experiment.

Which has the greater albedo – the white sand or the black sand?

Give examples of albedo on the Earth’s surface, one with high albedo, one with low albedo.

High: _________________ Low: _____________________

Here in South Florida, is it better to have a light colored roof or a dark colored roof? Explain your answer.

20

22

24

26

28

30

32

34

36

38

40

42

44

46

48

50

0 1 2 3 4 5 6 7 8 9 10

Temperature (°C)

Time (min)

Sketching Assignment – Global temperatures, Solar Radiation, Insolation and Albedo 5

C Experiment to illustrate differential heating of land and water

Fill one of the two beakers provided three-quarters full with room temperature water and the other three quarters full of dry, white sand. Suspend a thermometer in each beaker so that the top of each bulb is just below the surface (do this with masking tape – your Teaching Assistant will show you how).

Suspend the light over the two beakers so they are equal distances form the light.

Record the starting temperature in each beaker in the table. Turn on the light and record the temperature in each beaker every minute for 10 minutes. Record the temperatures in the table provided.

See the file named “Differential Heating Results” in the assignment dropbox for the temperature

values.

Start

temp

1 min 2 min 3 min 4 min 5 min 6 min 7 min 8 min 9 min 10 m

Water

Sand

How does the temperature of dry sand and water differ when they are exposed to radiation from the lamp?

Suggest a reason why the sand and the water may heat differently?

What does this experiment tell you about the observations made in the ApprenNet assignment?

How does the temperature of dry sand and water differ when they are exposed to radiation from the lamp? Suggest a reason why the sand and the water may heat differently?