Measuring the big-electric current and the big voltage is a difficult work in engineering measurement.
大电流、大电压的测量一直是困扰工程测量学的难题。
Often you see small and big wires, new and old, cheap and expensive electric cables that are useless, for until the current passes through them there will be no light.
你常常看到小的和大的电线，新的和旧的，便宜的和贵的电线都是没用的，只有当电流通过它们时才会有光。
Fuse is with melting point inferior material is made, electric current became big can calorific fusing, have insurance effect.
保险丝是用熔点较低的材料制作，电流大了会发热熔断，起到保险作用。
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