4.
某实验小组利用如图\((a)\)所示的电路探究在\(25{}^\circ {C}\tilde{\ }80{}^\circ {C}\)范围内某热敏电阻的温度特性。所用器材有:置于温控室\((\)图中虚线区域\()\)中的热敏电阻\({R}_{T} \),其标称值\((25^{\circ}C\)时的阻值\()\)为\(900.0{ }\Omega \);电源\(E(\)\(6\,{V}\),内阻可忽略\()\);电压表\(Ⓥ\)\((\)量程\(150\,{mV}\)\()\);定值电阻\({{R}_{0}}\)\((\)阻值\(20.0\ \Omega \)\()\),滑动变阻器\({{R}_{1}}\)\((\)最大阻值为\(1000\,\Omega \)\()\);电阻箱\({{R}_{2}}\)\((\)阻值范围\(0\tilde{\ }999.9\,\Omega \)\()\);单刀开关\(S\)\({\,\!}_{1}\),单刀双掷开关\(S\)\({\,\!}_{2}\)。实验时,先按图\((a)\)连接好电路,再将温控室的温度\(t\)升至\(80.0^{\circ}C\)。将\(S_{2}\)与\(1\)端接通,闭合\(S_{1}\),调节\({{R}_{1}}\)的滑片位置,使电压表读数为某一值\({{U}_{0}}\);保持\({{R}_{1}}\)的滑片位置不变,将\({{R}_{2}}\)置于最大值,将\(S_{2}\)与\(2\)端接通,调节\({{R}_{2}}\),使电压表读数仍为\({{U}_{0}}\);断开\(S_{1}\),记下此时\({{R}_{2}}\)的读数。逐步降低温控室的温度\(t\),得到相应温度下\({{R}_{2}}\)的阻值,直至温度降到\(25.0^{\circ}C\)。实验得到的\({{R}_{2}}-t\)数据见下表。
\(t/\) \({}^\circ {C}\) | \(25.0\) | \(30.0\) | \(40.0\) | \(50.0\) | \(60.0\) | \(70.0\) | \(80.0\) |
\(R_{2}/Ω\) | \(900.0\) | \(680.0\) | \(500.0\) | \(390.0\) | \(320.0\) | \(270.0\) | \(240.0\) |
回答下列问题:
\((1)\)在闭合\(S\)\({\,\!}_{1}\)前,图\((a)\)中\({{R}_{1}}\)的滑片应移动到______\((\)填“\(a\)”或“\(b\)”\()\)端;
\((2)\)在图\((b)\)的坐标纸上补齐数据表中所给数据点,并做出\({R}_{2}-t \)曲线;
\((3)\)由图\((b)\)可得到\({R}_{T} \)在\(25{}^\circ {C}\tilde{\ }80{}^\circ {C}\)范围内的温度特性。当\(t=44.0{}^\circ {C}\)时,可得\({R}_{T} =\)______\(\Omega \);
\((4)\)将\({R}_{T} \)握于手心,手心温度下\({{R}_{2}}\)的相应读数如图\((c)\)所示,该读数为______\(\Omega \),则手心温度为______\({\,\!}^{\circ}C\)。