Experiment5

Anjusha.C

September 2015

1 AIM

Electrical resistivity of semiconductor and noble metal resistora) Measuring the temperature-dependency of a noble-metal resistorb) Measuring the temperature-dependency of a semiconductor resistorInstrument used: LD DIDACTIC

2 APPARATUS

Sensor-CASSY, CASSY Lab 2,Current source box,Temperature box,Temperaturesensor NiCr-Ni,noble metal resistor,Semiconductor resistor,Electric oven,Safetyconnecting box

3 THEORY

The temperature-dependency of the specific resistance R is a simple test formodels of electric conductivity in conductors and semiconductors. In electri-cal conductors, R rises with the temperature, as the collisions of the quasi-freeelectrons from the conduction band with the incomplete atoms of the conductorplay an increasing role. In semiconductors, on the other hand, the resistancedecreases as the temperature increases since more and more electrons move fromthe valence band to the conduction band, thus contributing to the conductivity.This experiment measures the resistance values of a noble-metal resistor and asemiconductor resistor as a function of the temperature. For the noble metalresistor, the relationship R = R0 · (1 + ·) (R0: resistance at = 0 C) is verifiedwith sufficient accuracy in the temperature range under study. For the semicon-ductor resistor, the evaluation reveals a dependency with the form R e E/2kT(k = 1.38·10-23 J/K: Boltzmann constant) with the energy band interval E.

4 PROCEDURE

The temperature box at Sensor-CASSY input A measures the temperature ofthe sensor in the electric oven. Insert the measuring tip into the hole on the

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back of the oven so that the tip is in direct proximity to the resistor element.The current supply box at input B registers the electrical resistance.

Carrying out the experiment·Load settings· Start the measurement with (a value pair is recorded for every temperatureincrease of 5 K)· Switch on the oven· Stop the measurement with at the latest when the temperature reaches 470 K(approx. 200 C)· Switch off the oven and remove the resistor· When the oven has cooled off repeat the measurement with a different resistor

5 Graphs

Resistance vs Temperature graph of a noble metal resistor

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Resistance vs temperature graph of a semi metal

6 CALCULATIONS AND INFERENCE

Noble metal resistorThe graph is linear implying that resistance of a noble metal increases with in-crease in temperature. The The temperature coefficient (alpha) of the resistorcan be determined from the slope of the graph. Slope of the graph =.4 /Kalpha = .004/KSemi metalThe graph has 1/T dependance implying that the resistance of a semi metal de-creases as a function of tempurature. R proportional to e (E/2kT ).Taking logarithm we get logR =logc E/2kT.From the graph taking 2 values of T and R E can be computed.Bandgap =.5eV

7 RESULT

The The temperature coefficient (alpha) of the resistor(Pt) is found to be .004/Kwhich agrees with the theoretical value of .00407/K and the band gap of thesemi metal is found to be .5eV which agres with the theoretical value of .47eVwithin the allowed error limits.

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