用来烧开水的铝壶底上，有几个凹凸不平的同心圆圈，利用所学的物_爱下问搜题

搜题请搜索小程序“爱下问搜题”

问题问答题

用来烧开水的铝壶底上，有几个凹凸不平的同心圆圈，利用所学的物理知识，说一说有什么作用．

答案

有同心圆圈壶底的表面积比平壶底的表面积要大些，在炉火相同的情况下，壶底表面积大能吸收更多的辐射热．壶底表面积大与水的接触面积也要大些，这有利于通过热传递的方式把壶底的热传给水，使水烧开得快些，因此，壶底有凹凸不平的同心圆圈的第一个作用是“增大受热面积”；再从力学方面考虑可知，第二个作用是“增强机械强度（耐用）”．

完形填空

I fell in love with Yosemite National Park the first time I saw it, when I was 13. My parents took us there for camping. On the way out, I asked them to wait while I ran up to E1 Capitan, a ___16___ rock of 3,300 feet straight up. I touched that giant rock and knew ___17___ I wanted to climb it. That has been my life’s passion (钟爱) ever since--- ___18___ the rocks and mountains of Yosemite. I’ve long made Yosemite my ___19___.
About 15 years ago I started seeing a lot of ___20___, like toilet paper, beer cans, and empty boxes, around the area. It’s ___21___ me why visitors started respecting the place ___22___ and treated such a beautiful home-like place this way.
I tried ___23___ trash(垃圾)myself, but the job was too big. I would ___24___an hour or two on the job, only to find the area trashed all over again weeks later. Finally, I got so ___25__ it that I decided something had to change.
As a rock-climbing guide, I knew ___26___about organizing any big event. But in 2004, together with some climbers, I set a date for a ___27___. On that day, more than 300 people ___28___. Over three days we collected about 6,000 pounds of trash. It was amazing how much we were able to ___29___. I couldn’t believe the ___30___ we made ---the park looked clean!
Each year volunteers come for the cleanup from everywhere. In 2007 alone, 2,945 people picked up 42,330 pounds of trash and ___31___ 132 miles of roadway.
I often hear people ___32___ about their surroundings. If you are one of them, I would say the only way to change things is by ___33___ rather than complaining. We need to teach by ___34___. You can’t blame others ___35___ you start with yourself.

A．immediately

A．throwing away

C．breaking down

D．digging out

A．satisfied with

B．delighted in

A．dropped out

C．looked around

D．called back

C．questioning

B．explanation

单项选择题

以（）为中心是兴国之要，是我们党、我们国家兴旺发达和长治久安的根本要求。

A.经济建设

B.建设小康社会

C.建设和谐社会