(1)P=U 20 R0 =(6V)2 30Ω =1.2W;答:报警器R0的实际电功率是1.2W.(2)电路电流I=U R0 =6V 30Ω =0.2A,压敏电阻两端电压Ux=U-U0=8V-6V=2V,压敏电阻阻值Rx=UX I =2V 0.2A =10Ω,答:压敏电阻RX的阻值是10Ω.(3)由RX-F图象可知,当RX=10Ω时,压力F=20N, 受力面积S=1cm2=1╳10-4m2压敏电阻受到的压强P=F S =20N 1×10?4m2 =2╳105Pa;答:压敏电阻受到的压强是2╳105Pa.