（1）电源电压U=U1=I1R1=0.3A×10Ω=3V；（2）流过电阻R2的电流I2=IA2-IA1=0.5A-0.3A=0.2A，电阻R2的阻值R2= U I2 = 3V 0.2A =15Ω；故答案为：3；15．
