10.BC 11.BD Р二、填空题Р 12. (1)①Р 14.28 Ω; ③ D Р (2)①РAРVР— 0.6 3Р— 3 15РAРBР②不能Р理由:电源电压3V,导线、电源或电流表都有电阻,灯泡两端的电压达不到3V;或答最小电流不能达到0.02AР13.其他方法只要合理,能够得出正确结论,即可得分Р(1)F = = =80(N)= FNРF压=G人-FN =560-80= 480(N)Рp面= = =1.2×104(Pa)РG0 = nF-GA=3×80= 30(N)Р(2)h1 = = =2(m)Рv绳= n vB= n=3×=0.15(m/s)РF ´= = = 150(N)Р∵F ´ = 即150= ∴F浮=50(N) РVB = V排= = = 5×10ˉ3(m3)РρB= = = 9.4×103(kg/m3)Р5. 其他方法只要合理,能够得出正确结论,即可得分РUР甲РR1 РUР乙РR1РR2РAРR3РR2РV1РUРV2РR1Р丙Р(1)当开关S1、S2都闭合时,等效电路如右图甲: РU= I1 R1=1.5 R1 Р当只闭合开关S2时,等效电路如右图乙:РU= I2(R1+ R2)= 0.5(R1+ R2) R2=2 R1 Р开关都断开后,调节滑动变阻器的滑片在某点A时,等效电路如右图乙:V1的测的是R1、R2两端的电压,V2的测的是R2、R3两端的电压,РU1:U2=I (R1+R2):I (R2+RA) =3:4 РRA= R2=2 R1 РI1 R1= I(R1+ R2+ RA)РI=0.3(A) Р (2)当开关S1、S2都断开时,调节滑动变阻器的滑片至在最下端B点时,РP总= UI РU== =15(V) РR1= ==10(Ω) РRA=20(Ω) РIA2 RA= I32 R3Р0.32 ×20= 0.22 R3РR3=45(Ω)
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