【单选题】下列关于铀矿的描述不正确的是()
C.
地壳中总埋藏量比金、银少,化学性质不活泼,开采相对困难
【判断题】渗碳体Fe3C非常脆且非常硬,它的含碳量是6.69%,所以铸铁含碳量超过6.69%几乎没有应用价值
【判断题】渗碳体是铁与碳形成的金属间化合物,其含碳量为6.69%,质硬而脆,耐蚀性强,经4%硝酸酒精浸蚀后,渗碳体任呈亮白色,而铁素体浸蚀后呈灰白色,由此可区别铁素体和渗碳体。
【单选题】With a purely _____ load the voltage and current are in phase, giving a power factor of one.
【判断题】渗碳体是铁与碳形成的金属化合物,碳含量是6.69%,具有复杂的晶体结构。
【单选题】Why is it desirable to operate paralleled AC generators at the same power factor?()
A.
Circulating currents are kept to a minimum
B.
Field excitation losses are kept to a minimum
C.
Generator rotors will have a lesser tendency to hunt
D.
Because a power factor increase will decrease kilowatt output