1) using a laboratory stand so that the ends of the sheets are several centimetres above the table (Fig. (oC) Thermal Conductivity. Thermosensitive film with temperature range from 25 °C to 30 °C, three different metal plates of the same size, container for hot water, kettle. It is not necessary to use hot water to heat the sheets. If there are truly gifted physicists in the class, they can object that this argument is not entirely satisfactory – the sheets have different density and hence the mass, which affects the size of the heat needed for the heating, is also different. At higher temperatures, a large amount of hot vapour is generated and it flows upward affecting the measurement with thermosensitive films and making it unreliable. The film used in this experiment is black at temperatures lower than 25 °C. It is apparent that the copper sheet heats the fastest, followed by aluminium and brass. Then submerge the ends of the metal sheets in a mixture of water and ice. Thermal conductivity for aluminum is 215 W/ (m K) (from the table above). The thermal conductivity of a material such as metal is highly dependent on composition and structure. Watch how quickly individual cubes melt (the video is speeded 32 times): It is apparent that ice melts the fastest on a copper sheet, and the slowest on the brass sheet. A table with thermal conductivities (at 25 °C) of used metals is stated below: Thermosensitive film can be found on the internet under the name reversible temperature label. Fasten the copper, aluminium and brass sheet parallel to each other (see for example Fig. K). The effect of different thermal conductivity can be demonstrated not only with heating the metals, but also with cooling them. -73. (Similar metal plates can be obtained in designer tools store.) Copper has high thermal conductivity and therefore is able to constantly supply heat from the peripheral parts of the sheet to the place cooled by the ice cube. A successfully performed experiment is illustrated by the video below. Let all three metals warm up, for example on a radiator, until the thermosensitive films are navy blue. (W/m K) Aluminum. In the interpretation of the extension of the experiment, we should be careful not to give the impression that the sheets “sucked” the cold out of the ice – it is always necessary to interpret the temperature decrease as a heat extraction. See theory in an already described experiment: Thermal Conductivity of Plastic and Metal I., Theory. h�b```�@.uA�� ��+�z�77HZ�80^��1����X R����b�S?��+���*� Choose required ranks and required tasks. ��z��)�w�b�JEG���IG3���-���l�с� c`�d�y���bF=�@Ɨl���k�GJ�-�"��('��iX�$��g �}x�/)�U!�̕pQY�#�Q�`� w�: Figure 1 shows a tool made especially for this experiment to study the different thermal conductivity of metal – three different metal plates are partly covered by a thermosensitive film, which indicates the temperature increase. The temperature represented by the colour depends on the film type. 2). - t -. Then submerge the ends of the metal sheets in a mixture of water and ice. Put a container under these ends and pour hot water into it so as to cover the ends of the sheets. This article will explore the mechanisms of heat transfer, what makes metals ideal thermal conductors, and uses of common metals & alloys. Temperature. This is several times the value for steels (11 The advantage of this experiment is the possibility to go without the thermosensitive films. The description of the development of this experiment leads the students to a conclusion that “copper heats faster than aluminium” etc. More proficient students can figure out that we have already discussed the “willingness” of matter to change temperature in the context of specific heat capacity c of matter. } ��A�3 Rr#�d\�$�'00M~6������� 36 237. The disadvantage is that it is more time demanding (approximately 15 minutes). Tools and equipment usually found at schools, Thermal Conductivity of Plastic and Metal I., Theory, Change in Internal Energy by Performing Work: Nail Hammering, Conversion of Kinetic Energy into Internal Energy: Blow with a Mallet, Conversion of Kinetic Energy to Internal Energy: Falling Weight, Experimental determination of Specific Heat of Water, Comparing Specific Heat of Water and Vegetable Oil. Comparing Thermal Conductivity of Copper, Aluminium and Brass. Thermal Conductivity of Plastic and Metal II. 107 0 obj <>/Filter/FlateDecode/ID/Index[93 36]/Info 92 0 R/Length 85/Prev 181608/Root 94 0 R/Size 129/Type/XRef/W[1 3 1]>>stream Thermal conductivity (cal/sec)/(cm 2 C/cm) Thermal conductivity (W/m K)* Diamond... 1000: Silver: 1.01: 406.0: Copper: 0.99: 385.0: Gold... 314: Brass... 109.0: Aluminum: 0.50: 205.0: Iron: 0.163: 79.5: Steel... 50.2: Lead: 0.083: 34.7: Mercury... 8.3: Ice: 0.005: 1.6: Glass,ordinary: 0.0025: 0.8: Concrete: 0.002: 0.8: Water at 20° C: 0.0014: 0.6: Asbestos: 0.0004: 0.08: Snow (dry) 0.00026... Fiberglass: 0.00015: 0.04: … If you wish to filter only according to some rankings or tags, leave the other groups empty. The video is speeded 8 times. If the temperature increases, in the interval from 25 °C to 30 °C the film gradually changes its colour from brown, green and blue to navy blue, and finally after exceeding 30 °C the colour changes back to black. %%EOF If you perform this experiment in the summer, it is recommended to make sure that the temperature in the classroom is lower than the minimum temperature measured by the film (here 25 °C). Do not pour boiling water in the container, use water with temperature of 60 °C. Aluminum alloys can have much lower conductivities, but rarely as low as iron or steel. The effect of different thermal conductivity can be demonstrated not only with heating the metals, but also with cooling them. Thermal Conductivity of Plastic and Metal I. The table of contents will list only tasks having one of the required ranks in corresponding rankings and at least one of the required tags (overall). Fortunately, the densities of copper and brass are similar enough so that different behaviour of these two substances cannot be explained in other way than on the basis of different thermal conductivity. In a sample experiment, copper, aluminium and brass plates of the same dimensions are used; the thickness of the plates is 0.3 mm. This ability is significantly worse in the brass sheet. h��W�O�8�W�#����j��:�5m���ִ�I�* �����$%)����*rc�~����Q�P�h�C�>��1� ߜe� �|bR�&1M�o���@#�pRp��L�"5h�hÕO�c��TDKðP�� �Q:&�ƅ�E����D4�����-8��=. Thus the longer part of the measured metals can stay in a horizontal position. 128 0 obj <>stream However, you always need to ensure that the sheets warm up evenly. The goal of this experiment is to use thermosensitive films to visualize the different dynamics of heat conduction in three different metals. 93 0 obj <> endobj Metals are typically known to be highly efficient thermal conductors . Copper cools down the fastest, followed by aluminium and brass. If the classroom temperature is higher, the film changes colour to the corresponding temperature making the result less evident.
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