初三物理(人教版)電阻的測量（第二課時）2

電阻的測量（第二課時）年級：九年級學(xué)科：物理（人教版）主講人：覃凌學(xué)校：北京師范大學(xué)附屬實驗中學(xué)電阻的測量（第二課時）年級：九年級學(xué)科：物理（人教版）主講人：覃凌學(xué)校：北京師范大學(xué)附屬實驗中學(xué)RX153V5100115032伏安法測電阻原理：R=

UI場景一153V5100115032153V15100115032153V25100115032R0RXRX153V15100115032153V25100115032R0——I0

=U0R0IXI0RX153V15100115032153V25100115032R0等效轉(zhuǎn)換V1V2R0RXRX=

UXIX=

UXU0R0=

UXU0R0

UXU0=

UXI0S思考：R0RX153V5100115032153V25100115032R0RXR0153V5100115032場景二R0RX153V5100115032不允許拆改電路S1S2RX

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UXIX=

UXUR0UX=

UXUXUR0UXRXU

U?UXRXR0U

RXR0VS1S2RX=

UXIX=

30Ω=

10V6V×20Ω6V=

UXUXUR0設(shè)計思路：串聯(lián)電路或者局部短路RXR0VS1S2RXR0V1SV2場景三R0RXA130.61200.2300.60.4A230.61200.2300.60.4A230.61200.2300.60.4RXA130.61200.2300.60.4R0U0=I0R0153V5100115032A230.61200.2300.60.4RXA130.61200.2300.60.4R0I1I2RX=

UXIXI2R0

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I1=

I1U0A1A2RXR0S場景四R0RX不允許拆改電路A30.61200.2300.60.4S1S2A30.61200.2300.60.4A30.61200.2300.60.4A30.61200.2300.60.4RXR0A30.61200.2300.60.4RXR0S1S2RX

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UXIX=

I1R0

I1I2RXR0S1S2AI2I1I0RX

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I1R0

I1I2=

30Ω0.5=

AA×20ΩA0.20.2RXR0S1S2AI2I1R0RXS2設(shè)計思路：并聯(lián)電路S1A思考：有沒有不需要計算

就可以測量出未知

電阻阻值的方法呢？場景五RXA30.61200.2300.60.4S1S2RXS調(diào)節(jié)電阻箱，使甲、乙兩圖中的電流表示數(shù)相等，可以得出什么結(jié)論呢？甲圖乙圖RX=R0AAR0SAR0RXS1S2RXU圖1IR0U圖2I等效替代法AR0RXS1S2S課堂小結(jié)用電壓表測量用電流表和已知阻值的定值電阻獲得153V5100115032R0A30.61200.2300.60.4R=

UI課堂小結(jié)用電流表測量用電壓表和已知阻值的定值電阻獲得A30.61200.2300.60.41