128 0 obj
93 0 obj
(oC) Thermal Conductivity. 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. Let all three metals warm up, for example on a radiator, until the thermosensitive films are navy blue. - k -. %PDF-1.6
However, you always need to ensure that the sheets warm up evenly. Thermosensitive film with temperature range from 25 °C to 30 °C, three different metal plates of the same size, container for hot water, kettle. 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. 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 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. This is several times the value for steels (11 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. 1) using a laboratory stand so that the ends of the sheets are several centimetres above the table (Fig. The purpose of such colour changing of these films is not to attempt precise temperature measurements at a particular point, but rather to indicate and demonstrate the distribution of surface temperature.
This article will explore the mechanisms of heat transfer, what makes metals ideal thermal conductors, and uses of common metals & alloys. -73. The advantage of this experiment is the possibility to go without the thermosensitive films. h�b```�@.uA�� ��+�z�77HZ�80^��1����X R����b�S?��+���*� The film used in this experiment is black at temperatures lower than 25 °C. If the classroom temperature is higher, the film changes colour to the corresponding temperature making the result less evident. 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 for aluminum is 215 W/ (m K) (from the table above). 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
Observe the thermosensitive films change colour. See theory in an already described experiment: Thermal Conductivity of Plastic and Metal I., Theory. 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). endstream
94 0 obj
95 0 obj
<>/Font<>/ProcSet[/PDF/Text/ImageC]/XObject<>>>/Rotate 0/TrimBox[0.0 0.0 504.0 720.0]/Type/Page>>
96 0 obj
Thus the longer part of the measured metals can stay in a horizontal position. 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. • The thermal conductivity of aluminum and its alloys, which is 88 to 251 W/m K, or 51 to 164 Btu (h ft F), and increases with increase in temperature (Ref 1.4). 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 goal of this experiment is to use thermosensitive films to visualize the different dynamics of heat conduction in three different metals. If you wish to filter only according to some rankings or tags, leave the other groups empty.