两根由同种材料制成的均匀电阻丝A、B串联在电路中，A的长度为L，直径为d； B的长度为2L，直径为2d，那么通电后，A、B在相同的时间内产生的热量之比为
A．QA：QB＝2：1 B．QA：QB＝1：1
C．QA：QB＝1：2 D．QA：QB＝4：1
A
考点：
专题：恒定电流专题．
分析：串联电路电流相等，根据电阻定律R=ρ
求出电阻比，再根据Q=I2Rt求出A、B在相同的时间内产生的热量之比．
解答：解：长度比为1：2，直径比为1：2，则横截面积比为1：4，根据电阻定律R=ρ知，电阻之比为2：1，根据Q=I2Rt，电流相等，则热量之比为2：1．故A正确，B、C、D错误．
故选A．
点评：解决本题的关键知道串联电路电流相等，以及掌握电阻定律R=ρ 和焦耳定律Q=I2Rt．
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