3.7 Heat radiation and greenhouse effect. Task. How can one demonstrate the greenhouse effect?

Transcription

1 Science - Applied Science - Renewable Energy - 3 Heat Energy from Solar Energy (P953700) 3.7 Heat radiation and greenhouse effect Experiment by: Phywe Printed: Oct 7, 203 :52:05 AM intertess (Version 3.06 B200, Export 2000) Task Task How can one demonstrate the greenhouse effect? Use the space below for your own notes. Logged in as a teacher you will find a button below for additional information. - -

2 Additional information This experiment explains the principle of the greenhouse effect. At a surface temperature of about 5600 C, the sun mainly irradiates heat radiation in an area of 500 nm in the direction of the Earth direction. The terrestrial atmosphere allows the radiation of this wavelength pass almost completely to the earth's surface and heats it up on average at about 30 C. The Earth's surface reflects back into the atmosphere mainly infrared radiation of the wavelength 0,000 nm (Wien's displacement law). Nevertheless, radiation of this wavelength is absorbed to a large part by the greenhouse gases (like CO2). The greenhouse gases, on the other hand, reflect heat radiation in the direction of earth's surface which heats it up additionally. This effect is called greenhouse effect. The name is to be led back on the fact that one finds the same principle also in a greenhouse, the "Earth s atmosphere" of the greenhouse is represented by the glass window. In the experiment, the global warming of the Earth is shown via a black beaker with hot water. The greenhouse gases are substituted by a thin plastic disc. The temperature of the water is controlled using a thermometer. The heat radiation delivered by the black beaker is measured by means of a thermo generator, (once with and once without the plastic disc) during the path of rays. The greenhouse effect can be observed in this process. Notes on the Setup and Procedure The foamed plastic box of the solar collector is used for the isolation of the black beaker containing the hot water. At the same time, it is also its holder and the holder for the plastic disc in this experiment. Beyond it, it also delivers additional protection from external disturbances of the sensitive temperature measurement. It is important to notice that at the beginning of the measurements the amount of the thermo is less than 0.5 mv. If it is not possible to reach this value after long time, this is due to the fact that the front plate of the Peltier element is exposed to other influences. Then it should be made sure that no warm objects are near the experiment set-up and that the windows are closed in order to have as little air circulation as possible in the classroom as possible

3 Material Material - 3 -

4 Material from "TESS advanced Applied Sciences Renewable Energy, EN-BS" (Order Nr ) Position No. Material Support base, variable Order No Quantity 2 Support rod, stainless steel, 8/8, l = 600 mm, d = 0 mm Solar collector for student experiments Thermogenerator for student experiments Beaker, black Lab thermometer, C Slide mount for optical bench Beaker, 00 ml, low form, plastic Glass beaker, DURAN, short, 400ml Stopwatch, 24h, /00 s & s Connection cord, 32 A, 250 mm, blue Connection cord, 32 A, 250 mm, red Double socket, pair, red and black Measuring tape, l = 2 m Additional Material 5 Digital multimeter, 3 /2-character display Hot water Material required for the experiment - 4 -

5 Setup Setup Screw the four splited support rods together to get two long ones (Fig.). Set up the tripod bank using both support rods and the variable support base (Fig. 2 and Fig. 3). Fig. 2 Fig. Fig. 3 Open the solar collector and remove the small piece of foamed plastic (fig. 4)

6 Fig. 4 Place the rider and the solar collector on the optical bench according to fig. 5. The distance between the rider and the solar collector should be 5 cm. Fig. 5 The thermo generator is made up of an aluminium block, a Peltier element and a yellow clip. Fasten the black plate to the thermo generator by means of the yellow clip, in doing so the Peltier element must be laid crosswise so that the circuits point out to the side (fig. 6 and 7). Fig. 6 Fig. 7 Put the thermo generator on the rider (fig. 8)

7 Fig. 8 Now connect the thermo generator to the multimeter using both double sockets and both additional cables, and then set the DC voltage measuring range at 200 mv (fig. 9 and fig. 0). Fig. 9 Fig

8 Action Procedure Let your teacher pour hot water in the glass beaker. Afterwards fill the black beaker with 30ml of hot water by means of the small measuring cup (fig. ). Fig. Measure the temperature of the water in your beaker with the thermometer. When the water cools down to about 55 C, put the beaker in the middle of the solar collector, so that it touches the rear wall and introduce the thermometer into the water through the hole on the top of the solar collector (fig. 2). Fig. 2 Close the solar collector with the plastic disc. Now start the stopwatch, measure the water temperature ϑ and the voltage U of the thermo generator at every full minute (time t). Write down the measured values in table (fig. 3). Finish the measurement after 5 minutes

9 Fig. 3 Open the solar collector for cooling, take the beaker from the solar collector and pour out the water. Wait until the voltage of the thermo generator goes down under 0.5mV. Now repeat the experiment without plastic disc. Tip In both measurements the water should have the same initial temperature in order to be able to compare better the results with each other

10 Results Results t in min ϑ in C Table Measurement on the plastic disc U in mv Typical Results Measurement on the plastic disc t in min ϑ in C 49,0 48,5 48,0 47,5 47,0 U in mv 0,6,2,8 2,2 2,6-0 -

11 t in min ϑ in C Table 2 Measurement without the plastic disc U in mv Typical Results t in min ϑ in C 49,5 48,5 47,5 47,0 46,0 Measurement without the plastic disc U in mv 3,0 3,9 4,4 4,6 4,7 - -

12 Evaluation Evaluation Question What can you observe in both measurements? Answer In both measurements the voltage first increases fast. In the measurement without the plastic disc the voltage has already estabilised at a saturation value after 5 min. In the measurement with the plastic disc can also be observed that the voltage values do not increase as fast as at the beginning after 5 min. They should also here approach to a saturation value. Wecan observe that this saturation value is higher in the measurement without disc than in the measurement with disc. Question 2 Why does the voltage in the thermo generator increase, when one puts the beaker with hot water in its nearness? - 2 -

13 Answer The heat radiation from the beaker heats up the front plate of the Peltier-Element causing a thermo voltage in it as a result. Question 3 How do you explain the difference between the measured voltages without and with the plastic disc? Answer The plastic plate absorbs and reflects part of the heat radiated by the beaker. In this case, less heat radiation hits on the Peltier element, therefore it heats up less. Also a lower tension is missed as well. Question 4 Which effect - appearing on the Earth - is produced hereby? Which role do the beaker with hot water and the plastic disc play? - 3 -

14 Answer This effect causes the greenhouse effect on the Earth. The plastic disc plays the role of the greenhouse gas in this experiment. The beaker represents the global warming of the Earth