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【简答题】
氧气的制法 （1）工业上根据氧气和氮气的______不同，分离液态空气得到氧气． （2）实验室制取氧气的方法 a：加热高锰酸钾反应的文字表达式：______ b：双氧水分解反应的文字表达式：______ （3）收集方法 氧气______溶于水，可以用排水法；氧气密度比空气略大，也可以用______法． （4）氧气的检验将带火星的木条______集气瓶______，木条复燃，证明是氧气． （5）写出氧气的验满的操作方法、现象、结论．______．
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【简答题】有一批半径为1cm的球,为了提高球面的光洁度,要镀上一层铜,厚度定为0.01cm,估计每只球需用铜 g 。(计算结果保留2位小数,铜的密度是 )
【单选题】A circuit breaker differs from a fuse in that a circuit breaker
A.
melts and must be replaced
B.
is enclosed in a tube of insulating material with metal ferrules at each end
C.
gives no visual indication of having opened the circuit
D.
trips to break the circuit and may reset
【简答题】有一批半径为 1cm 的球 , 为了提高球面的光洁度 , 要镀上一层铜 , 厚度定为 0 . 01cm . 估计一了每只球需用铜多少 g ( 铜的密度是 8. 9g/cm 3 )?
【单选题】Ice-breaker assistance for convoy will start at 1930UTC
A.
Ice-breaker assistance for fleet passage stared at 1930UTC
B.
Ice-breaker assistance for fleet passage is due to start at 1930UTC
C.
Ice-breaker assistance for M.V. Convoy started at 1930UTC
D.
Ice-breaker assistance for M.V. Convoy is due to start at 1930UTC
【单选题】A circuit breaker differs from a fuse in that a circuit breaker （）.
A.
melts and must be replaced
B.
is enclosed in a tube of insulating material with metal ferrules at each end
C.
gives no visual indication of having opened the circuit
D.
trips to break the circuit and may be reset
【简答题】有一批半径为1cm的球,为了提高球表面的光洁度,要镀上一层厚度为0.01 cm的铜.已知铜的密度为8.9 g/cm 3 , 试估计一下每个球需用多少克铜?(精确到0.01)
【单选题】The purpose of a main switchboard circuit breaker's reverse power trip is to _____.
A.
prevent main circuit overload
B.
protect the circuit breaker blowout coil
C.
prevent alternator motorization
D.
prevent low voltage tripout
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