Question

Un filament incalzit la 2000° C are rezistenta de cinci ori mai mare decat la rece(0°C). Coeficientul termic legat de cresterea rezistivitatii cu temperatura este? A. 10 la -3 x k la -1
B. 10 la 3 x k la -1
C 2 x 10 la -3 x k la -1
D 2 x 10 la 3 x k la -1

Answer 1

[tex]\displaystyle Se~da:\\ \\ \Delta t_1=2000^\circ\\ \\ \Delta t_2=0^\circ\\ \\ R_1=5\times R_2\\ \\ \alpha=?K^{-1}\\ \\ \\ Formule:\\ \\ 1)R_1=R_0\times (1+\alpha\times\Delta t_1)\\ \\ R_0=\frac{R_1}{1+\alpha\times\Delta t_1}\\ \\ \\ 2)R_2=R_0\times (1+\alpha\times\Delta t_2)\\ \\ R_0=\frac{R_2}{1+\alpha\times\Delta t_2}\\ \\ \\ [/tex]


[tex]\displaystyle Egalam:\\ \\ \frac{R_1}{1+\alpha\times\Delta t_1}=\frac{R_2}{1+\alpha\times\Delta t_2}\\ \\ \frac{5\times R_2}{1+\alpha\times\Delta t_1}=\frac{R_2}{1+\alpha\times\Delta t_2}\\ \\ \frac{5}{1+\alpha\times\Delta t_1}=\frac{1}{1+\alpha\times\Delta t_2}\\ \\ 5+5\times\alpha\times\Delta t_2=1+\alpha\times\Delta t_1\\ \\ \alpha\times\Delta t_1-5\times\alpha\times\Delta t_2=4\\ \\ \alpha\times(\Delta t_1-5\times \Delta t_2)=4\\ \\ \alpha=\frac{4}{\Delta t_1-5\times \Delta t_2}\\ \\ \\[/tex]


[tex]\displaystyle Calcule:\\ \\ \alpha=\frac{4}{2000-5\times 0}=0,002K^{-1}=2\times 10^{-3}K^{-1}\\ \\ \\ Raspuns:~c). [/tex]