桌面上有下列器材:学生电源(电压不变)、滑动变阻器、电阻箱(符号 )、已经调零的电压表和电流表、开关、导线若干.请你设计一个实验证明:电流一定时,电阻两端的电压与电阻阻值成正比.要求:写出实验电路、实验步骤、实验记录表.
解:
(1)由分析可知,可以利用电阻箱改变电路中电阻,滑动变阻器与其串联调通过变阻箱电流不变,电压表和电流表分别电阻箱的两端电压和通过的电流,电路图如图所示:
材料一:江南地域辽阔而人烟稀少;稻米和鱼是主要食物,人们还可以从山中采集植物果实和贝类为食;放火烧荒,耕种水田;不需要商人贩卖货物,没有非常富裕的人。──西汉《史记》材料二:江南……地广野丰,民勤本业,一岁或稔(rěn,丰收),则数郡忘饥。……丝绵布帛之饶覆衣天下。──南朝 《宋书》(1)分析比较以上两则材料,说明江南地区从西汉到南朝发生了怎样的变化?(2)发生这样的变化的最根本的原因是什么?此外江南地区还有哪些优势?(3)这种变化对我国经济产生了怎样深远的影响?
小芳给你一个如图所示的量角器,如果你用它来度量角的度数,那么能精确地读出的最小度数是( )
根据括号内的英(汉)语提示,完成句子。⑴Nothing can prevent us from ____ (realize) our “Chinese Dream”. ⑵Unfortunately he had his left leg____ (break) in the high jump last week.⑶My grandmother often falls____ (睡着) when she watches TV.⑷Tom____ (write) his lessons when he heard a terrible noise outside.⑸Mary has curly hair and she is of medium____ (高度).⑹Lucy often____ (刷) her teeth after meals.⑺We have walked for a long time. Let’s stop____ (have) some water.⑻—____you ever____ (be) to an amusement park? —Yes, I have.⑼— What kind of noodles would you like ? — I'd like some____ (牛肉) and tomato noodles, please.