题干

设图是某几何体的三视图,则该几何体的体积为(  )

A:

B:

C:

D:

上一题 下一题 0.0难度 选择题 更新时间:2019-11-25 04:46:31

答案(点此获取答案解析)

D

同类题1

阅读短文,回答问题:

    电热膜是一种新型的电热器件,如图甲所示是一种常见的电热膜.电热膜是在绝缘的聚酯薄膜表面,经过特殊工艺加工形成的一条条薄的导电墨线,导电墨线两端与金属导线相连,形成网状结构,其内部结构如图乙所示.

    电热膜通电工作时没有发红、炽热现象产生,它与被加热物体直接接触,产生的热量很快传给被加热物体,所以电热膜本身温度并不太高,不易氧化,使用寿命长.在制造电热膜时,会出现不同区域导电墨线厚度不均匀的现象,厚的导电墨线电阻小.导电墨线电阻随温度变化的关系如图丙所示,这种温度特性的优点是,它不会因厚度不均匀而出现严重发热不均、局部过热的现象,这是电热丝所不具备的,它保证了电热膜各处的温度均匀.

(1)电热膜取暖器工作时,室内空气温度升高是通过____ 方式增加空气内能的;

(2)某根导电墨线的局部导电材料脱落,如图丁中A部分,这根导电墨线的电阻____ ;

A.变大     B.变小     C.不变     D.以上三种情况均有可能

(3)与传统的电热丝加热器相比,电热膜取暖器的发热效率高,原因是____ 

(4)将图戊中一块电热膜接入电路,正常工作时金属导线中A、B处电流分别为IA和IB,则IA____ IB;(填“<”、“=”或“>”)

(5)电热膜不会因厚度不均而出现局部过热的现象,原因是____ 

同类题5

阅读理解

    It was a hot,humid day, and my brother Walt and I had decided that the only way to surviveit would be to go swimming in a deep swimming hole across Mr. Blickez's pasture(牧场) and through some woods.

    The onlyproblem with our plan was that this pasture was guarded by a huge, meanHereford bull. Mr. Blickez had told us that Elsie was the meanestbull in the township, maybe even the county, and we believed him. But the hotter it got, the more we thoughtthere was something fishy about his claim. For one thing, we remembered Mr. Blickez liked telling tall tales; for another, Elsie seemed like an oddname for a bull.

    Finally, Italked Mom into asking permission for us to walk through the pasture, but thenanother problem surfaced.Mom said she would talk to Mr. Blickez if we would take our cousin Joanie along with us. Joanie was almost two years older than me anda head taller. If her teasingever got around my grade school, it would be all over for me. In fact, I still had a headache from a quarrelwith her that morning.“I'm not goingswimming with that dumb girl cousin.” I told my mom.

  “Either Joaniegoes with, or you stay home alone,” Mom said in her serious tone. I gave in and we set out. On our way across the pasture, Walt yelledsuddenly. Elsie hadapproached him quietly and was licking(舔) his back. Joanie and Idove under the wire fence, but while I was on the ground I looked up and sawthat Elsie wasn't a big mean bull after all. She was going to keep licking my brother's back as long as he stoodstill.

    We had manygood days growing up and visiting our secret swimming hole guarded by theso-called “big mean bull”. And as it turned out, for a girl cousin, Joanie hasn't been too bad. She's been one of my best friends over theyears.