4-TEMP COEF OF RESISTANCE

# 4-TEMP COEF OF RESISTANCE - TEMPERATURE COEFFICIENT OF...

This preview shows pages 1–2. Sign up to view the full content.

10 TEMPERATURE COEFFICIENT OF RESISTANCE OBJECT To measure the temperature coefficient of both thermistors and copper wire. APPARATUS Thermistor assembly, copper wire assembly, electrically heated water bath, temperature sensor, slide-wire Wheatstone bridge, galvanometer, Power supply, resistance box, eight wires THEORY Most metals used as electrical conductors exhibit a linear relation between resistance and temperature. The temperature coefficient of resistance of such metals is defined by the expression = o o t tR R R (1) where t R : value of resistance of the metallic conductor at temperature t C o R : value of resistance of the metallic conductor at temperature 0 C Of course, equation (1) may be rewritten as R t = R o t + R o (2) when we recognize immediately that equation (2) is simply the slope-intercept form of a straight line, namely, y = mx+b. Thus, if we were to plot a series of values of resistance versus temperature for a given specimen, the resulting straight line would intercept the resistance axis at the value R o while the attendant slope divided by R o is the value of Most metals have a small positive temperature coefficient of resistance. In contrast with metals, thermistors have large negative temperature coefficients. Moreover, with thermistors the change of resistance with a change in temperature is non-linear. The resistance of a thermistor is given by the equation R = R a ) / 1 / 1 ( a t t where R: resistance in ohms at temperature t (K)

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
This is the end of the preview. Sign up to access the rest of the document.

## This note was uploaded on 08/25/2011 for the course PHYS 164 taught by Professor Johnjames during the Fall '09 term at MO St. Louis.

### Page1 / 4

4-TEMP COEF OF RESISTANCE - TEMPERATURE COEFFICIENT OF...

This preview shows document pages 1 - 2. Sign up to view the full document.

View Full Document
Ask a homework question - tutors are online