On the change in resistance during heating of metals. Scheme, description

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On the change in resistance during heating of metals. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Electrician's Handbook

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A school physics course describes how the resistance of conductors changes when heated - it increases. The coefficient of relative increase in resistivity during heating for most metals is close to 1/273 = 0,0036 1/°C (differences are within 0,0030...0,0044). How does the resistance of a metal change as it melts?

Figure 1 shows a graph of changes in the resistivity of copper during heating. As can be seen, at the melting temperature, a resistance jump of 2,07 times is observed. Thus, from normal temperature (20 ° C) to the melting temperature, the resistivity of copper increases by 5,3 times (coefficient K1), during melting it increases by another 2,07 times (coefficient K2), and only 10,82 times ( coefficient K3 = K1K2).

These coefficients are given for various metals in the table, where R is the resistance of a kilometer length of wire from a given metal with a cross section of 1 mm2; Tmelt is the melting point of the metal (metals are arranged in order of increasing resistance).

* Due to the special properties of nickel, data are not given (see below).
** Data not found.
*** The normal temperature for mercury is its melting point (-39°C). For nickel, the resistivity behaves very unusually (Fig. 2). At first, it increases, but only up to a temperature of 358°C, and then sharply decreases and at temperatures above 400°C it becomes less than at room temperature. Bismuth is a very unusual metal. Its specific resistance during melting decreases sharply, and so that the resistance of the molten metal is lower than that of the solid at room temperature.

You can also pay attention to the high value of the coefficient K1 for tungsten. That is why incandescent bulbs have a filament resistance at the moment of switching on many times less than in the operating mode (which is why they most often burn out).

See other articles Section Electrician's Handbook.

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