题目

将“PZ220-100”的灯泡与总电阻是121Ω的滑动变阻器串联起来,接到220V的电源上,如图9-9示,调整滑动变阻器的阻值时,可使电灯的功率在多大范围内变化? [分析]“PZ220-100”是指灯泡的额定电压220V和额定功率100w。当它与滑动变阻器串联后接入电路(图1)时,由于滑动变阻器的电阻发生变化,灯泡两端的实际电压和实际功率也随之变化。我们只要求出滑片在A,B两端点时灯泡的电压和实际功率即可。[答]滑片在 A端时, RAB=12lΩ,与灯泡串联,灯泡电——Why couldn’t they catch the 6:30 train ? ——Because they were delayed by          .A.some heavy traffics B.heavy traffic C.a heavy traffic D.any heavy traffic
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