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When the temperature has reached the boiling point, the valence band, and so this is referred to as hole conduction. of a commercial thermistor may change by an order of magnitude for a temperature This is known as a voltage divider. band is completely empty. The relationship turns out will drop accordingly. temperature of the semiconductor rises. What is Sensible Heat? and Engineers, Prentice-Hall (1991), pp. 3) What are some of the possible sources of error in this experiment 1 Beaker . Æ , 7$ 8$ H$ $ Æ , 7$ 8$ H$ a$ – Â ıı j µ Ô $ l € • – ¡ ¢ ¤ ¥ ¨ © À Á Â Ã ò ò å Ö ò ò Æ ¶ ° « © « © § © « © © ° $a$ Æ $ Æ 2á 7$ 8$ H$ a$ $ Æ 8ì 7$ 8$ H$ a$ $ Æ 7$ 8$ H$ a$ $ Æ 7$ 8$ H$ a$ $ Æ 7$ 8$ H$ a$ * 0 0 P °Œ. The resistance of the PTC thermistor should gradually and steadily rise, within seconds of being applied. When you apply heat to the body of a thermistor, its resistance should begin to steadily decline within seconds after heat is applied. Is your value for Eg reasonable, given that for many semiconductors Therefore the electrical resistance would fall as the ÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿì¥Á 7 ğ¿ Ã bjbjUU ú$ 7| 7| – , ÿÿ ÿÿ ÿÿ l D D D D \ \ \ \ h f2 ì ˆ ˆ ˆ ˆ ˆ §' §' §' å1 ç1 ç1 ç1 ç1 ç1 ç1 $ R3 r5 º 2 §' g' @ §' §' §' 2 —( D D ˆ ˆ ß! PURPOSE OF THE EXPERIMENT The aim of the experiment is to investigate how the resistance of a thermistor changes with temperature. to its resistance). a hole; electrons in the valence band can contribute to electric (You'll need to know that k = 8.617 X 10-5 eV/K.). Heater, dry blower, or any type of heating device. valence band to the conduction band, if the energy is at least as large WORK If possible use your thermistor to estimate the following temperatures: (a) inside a fridge (b) body temperature thermistor V mA Eye protection advised " l m n o Š ó ô Ü İ ˆ ‰ ” Ì Í Ò ç C D ] j ² ³ $ • – ¡ ¢ ¤ ¥ ¨ © À Ã ıîŞıÕ ıÕ Ó ÑÏ ıÕıËıÕıÂıÕıÂıÕı ¿ ¹ µ « 5�B*CJ \�phÿ 5�\� Is this what you see AND how would they affect the slope of your data? In this article, we go over how to test a thermistor- to check whether it is good or not. YOU WILL NEED A thermistor connected to leads that have been insulated with silicone jelly, a variable voltage d.c power supply (0 -12V), a milliammeter (0 - 100mA), a d.c voltmeter (0 -12v), a beaker of water, a thermometer (0 -100o C), a bunsen burner tripod, gauze and mat. • Using a multimeter to measure the resistance of a thermistor. If it is near its rated resistance value, then so far, it is good. to R. What does the slope of the graph give you? as a device for measuring temperature because small changes in temperature The • Investigating the variation of thermistor resistance with temperature. Also obtain an estimate of the uncertainty in your value for Eg In other words, higher energy states can be populated These electrons are no longer bound to a single atom, but rather PTC thermistors are thermistors whose resistance increases when the temperature it is exposed to increases. Since the thermistor is a variable resistor, we’ll need to measure the resistance before we can calculate the temperature. near room temperature the gap energy is on the order of 1 eV? From the band theory of solids, it is deduced that the constant B is material from which the thermistor is made. the temperature, the more charges (electrons in the conduction band and a significant change in the states available to the less tightly bound (A 6v battery pack can replace the power supply but then a variable resistor would also be needed). If it does not, then it is faulty. In a semiconductor the energy gap is of the order of 1 eV; at room temperature the corresponding voltage drop across the thermistor (which is proportional PURPOSE OF THE EXPERIMENT The aim of the experiment is to investigate how the resistance of a thermistor changes with temperature. We then use the ohmmeter to check the resistance after various stages of our testing All we need to test a thermistor is an ohmmeter or a multimeter that contains an ohmmeter. 381ff. 5�CJ \� CJ OJ QJ ^J aJ H*aJ 5�\�H*B*CJ aJ ph ÿ j 5�CJ UaJ mH nH uj CJ UaJ mH nH u aJ ' " # l p Š ó ô ˆ ‰ ” u Ñ Ò ç 2 F \ ] j ı ğ æ Ú Í Ë Í Í Ë Í Í Í ¼ ¼ Í Í Í Í Í Í Í $ Æ ş 7$ 8$ H$ a$ $ Æ 7$ 8$ H$ a$ Æ ÷Æ 7$ 8$ H$ It will then record 2) Rearrange the above equation to prove that it doesn't matter what You will measure the temperature dependence of the resistance of a thermistor, Heat the water and record readings of temperature, current and voltage roughly every 10o C. MEASUREMENTS TO MAKE For each value of temperature taken: Temperature of water (and thermistor) Ammeter reading (I) Voltmeter reading (V) CALCULATIONS Work out the resistance of the thermistor for each temperature value (V/I) and record them in your table. Draw sketch of bead, probe, disk, rod type thermistor. Pauli exclusion principle. be about 9.3KΩ. from the uncertainty in the slope of your fitted line. The resistance of the PTC thermistor should gradually and steadily rise, within seconds of being applied. Express Eg of ln(R) versus 1/T, obtain your measured value of the energy gap Eg. (Note that values of 1/T = 2 X 10-3 and 1/T = 3 X 10-3 large energy separation which is referred to as an energy gap. What is the maximum value of Thermistor resistance in the experiment? We will check this characteristic to see whether it behaves accordingly. The band of highest energy states is called with your data? Electrons If the resistance increases steadily, then the PTC thermistor is good. then it is good. If the resistance increases steadily, then the PTC thermistor is good. and hot plate. processing and graphing. to visualize a hole moving opposite the direction an electron moves in thermistor interfaced to personal computer, thermometer, beaker of water Robert A. 1 Multimeter . As the temperature is raised, some electrons to be exponential, as suggested by a graph of the logarithm of resistivity 1 Thermistor . respectively represent temperatures of 500 K and 333 K.), The linear relationship between the logarithm of resistivity and the This can be done either by a heater, dry blower, or any type of heating device. Now apply heat, just like before, to the thermistor's body. Testing a PTC thermistor follows all the same steps as a NTC thermistor. of occupied states in the conduction band, the semiconductor is said to In a manner similar to that for an atom, energy states in a solid are get enough thermal energy to "pop up" into the conduction band, in accordance become "communal property� of the whole solid, and they are able to move If it is, it is good. which you can export to a spreadsheet to analyze as described in the For The Arduino will measure the voltage at a point between the thermistor and a known resistor. 5. button when the temperature reaches a certain value. Thermistors are characterised by their base resistance as well as their “B” value. where k is Boltzmann's constant. a device made from an intrinsic semiconductor. 4. If the number of unoccupied states in the valence band equals the number The base resistance, for example, 10kΩ, is the resistance of the thermistor at a given temperature, usually 25 o C so is defined as: R 25. For example, the resistance 26 Jun, 2019. Measure the temperature of the water, the current shown by the milliammeter and the voltage shown by the voltmeter. So if heat is applied to a NTC thermistor, its resistance First check, with an ohmmeter, the thermistor without any heat applied. An unoccupied state in the valence band is called Hot water . to see if the thermistor is behaving according to the characteristics of the thermistor. the states are extremely close together, but between bands there is a comparatively Your Report section. change from 273 K to 373 K. You are provided with a commercial thermistor, which you can place in First, before applying any heat to the thermistor, check its rated value. A thermistor's primary function is to measure the temperature of devices.You must consider the determining base of thermistor resistance, as well as the current bias of the sensor. increases accordingly. currents by moving to fill the hole states. than its rated value, then the thermistor is faulty and should be discarded. but the states group into bands. A thermometer Materials : Copy of the lesson . NTC thermistors are thermistors whose resistance decreases when the temperature it is exposed to increases. An NTC thermistor, again, is a thermistors whose resistance decreases when the temperature it is exposed to increases. Measure the resistance of the thermistor from room temperature to 100°C.
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