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ａ．影响导体电阻的因素。①导体长度：将钨丝断了的白炽灯灯丝搭接好后与好灯泡接入照明电路，通电后观察两灯亮度发现：搭丝的灯泡较亮。分析：搭丝后导体长度减小；而亮度大的原因由Ｐ＝Ｕ２／Ｒ可知是Ｒ减小，使Ｐ实增大，可见导体长度减小，导体电阻减小。②导体的横截面
a. Factors that affect conductor resistance. 1 Conductor length: The incandescent filaments with broken tungsten filaments are lapped and connected to the lighting circuit with a good bulb. After the power is applied, the brightness of the two lamps is observed. Analysis: The length of the conductors after wiring is reduced; and the reason for the large brightness is P=U2/R. It can be known that R decreases, and P increases. It can be seen that the conductor length decreases and the conductor resistance decreases. 2 conductor cross-section