Most solids do expand when heated, and its length changes by an amount proportional to the original length and the change in temperature.

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1 A0-E-Y Experiment: Thermal Expansion Apparatus Purpose To use steam heating pot to generate steam. Make the steam flow through the metal rod to make it expand, and then use the dial indicator to measure the length of the metal rod after expansion in order to calculate the coefficient of linear expansion. Theory Most solids do expand when heated, and its length changes by an amount proportional to the original length and the change in temperature. L L0 L0αT () L L0 αt () In the equation, L0: the length at 0 L: the length at T α: the constant of proportionality, called the coefficient of linear expansion In the equation, L: the length at T L: the length at T So we obtain the equations below,

2 L =L 0 ( αt ) (3) L =L 0 ( αt ) (4) L T = L T L = L T - L - L The difference of L and L is minimal, so L ~ L, we obtain, L = L T T (5) (6) In the equation, L: L -L T: T -T Linear expansion coefficient is defined as the increment of length of a solid in a unit of length for a rise in temperature of at constant pressure. Instead of the increase of the length, but also consider the expansion in volume. By equation (), we obtain, V=V 0 ( βt) (7) In the equation, V 0 : the volume at 0 V: the volume at T β: the volume expansion coefficient Assume that the side length of a cube is L, the volume at T V= L 3 = 3 T = 3 L 3 o o should be, 3 3 L 3 T 3 T T Since α is a small number, and 3 can be gotten rid of in the equation, that is V= L 3 o (+3 T) (8) Compare equation (7) to equation (8), we know that the volume coefficient is three times the coefficient of linear expansion, soβ=3α. Although the conclusion above

3 But the volume of an object can be divided into many cubes, so for any solid, this conclusion is correct. Instrument Fig. NO Accessory Quantity Steam Generator Steam Heating Pot 3 Steam Heating Pot Lit 4 Fixer 5 Aluminum Rod 6 Metal Rod 7 Brass Rod 8 Base 3

4 9 Zeroing Knob 0 Metal Rod Supporting Base Dial Indicator Digital Electronic Thermometer 3 Thermometer Socket 4 Water Container 5 Steam Conduit Steam Generator HOW TO USE. Switch: this switch will illuminate when the heater starts heating.. Temperature control knob: temperature control protection switch. The generator starts to heat up when the knob is turned till the switch lights up but No Water Indicator doesn t. 3. No water indicator: the indicator lights up when in a non-heated or no water state. 4

5 A0-E-Y 4. Fuse reversion button: it trips when there is no water or overheating, push this button to turn it on again when the generator cools off. 5. Regularly clean the device using heated citric acid with water to maintain the efficiency. 6. Avoid getting water on sockets and switches. Procedure. Wear gloves when using the device since the temperature is very high.. Measure the original length of the metal rod and record. 3. Fill the pot 80 % full with water. The experiment set is shown as Fig.. 4. Make the metal Fig. of the metal bar and the other end to fit the end of the zeroing knob against the groove dial indicator as shown in Fig. 3. 5

6 Fig.3 4. Record the room temperature and the initial reading of the dial indictor. (start from 4 mm). 5. Turn the switch on to generate the steam. 6. When the steam is generated after 5 minutes, observe the thermometer and dial indicator. 7. When the temperature is stable, record the readings down ( at about 98 to 00 ) 8. Turn the zeroing knot to zero, and then change the metal rod when the metal rod and conduit cool off. Calculate the elongation of metal rod and the coefficient of linear expansion. 9. Replace the metal rod, and repeat steps 3 to 8. Experimental Record Coefficient of linear expansion of metal: α( 0-6 )/ C Substance gold silver Brass steel aluminum lead Coefficient of linear expansion

7 Brass: original length L = Temperature T T T initial reading Length (dial indicator) Elongation L mm Average value = Aluminum:original length L = Temperature T T T initial reading Length (dial indicator) Elongation L mm Average value = Unknown metal: original length L = Temperature T T T initial reading Length (dial indicator) Elongation L mm Average value = 7

8 Questions and Discussions. What causes the errors? 8

9 Atis Scientific Instruments Co.,Ltd Tel: Address:F., No.8, Nanming St., South Dist., Tainan City 70, Taiwan (R.O.C.) Website: 9