问题 问答题

小华在探究“平面镜成像的特点”的实验中:取两段等长的蜡烛A和B,点燃玻璃板前的蜡烛A,用眼睛观察,在此实验中:

(1)用透明的玻璃板代替平面镜是为了______

(2)他选择的蜡烛B和蜡烛A的大小,外形完全一样是为了______,实验时用B替代点燃蜡烛A的像,若观察到两者完全重合,可以说明______,这种研究问题的方法称为______.(选填“控制变量法”“等效替代法”或“类比法”)

(3)直尺的作用便于比较______的关系.

(4)移去蜡烛B,并在其所在位置上放一光屏,则光屏上______(选填“能”或“不能”)接收到蜡烛A的像,这说明平面镜成的是______像 (选填“实”或“虚”).

(5)如果把蜡烛A向镜后移运动一段距离,双移动蜡烛B去与A的比较,会发现蜡烛A像的大小将______(选填“变大”“变小”或“不变”)

答案

(1)实验中用透明的玻璃板代替平面镜,在物体的一侧能看到物体的像,同时透过玻璃板也能观察到代替物体的另一个物体,便于确定像的位置.

(2)当物体B和物体A的像完全重合时,便于比较物像大小关系.所以选择的蜡烛B与蜡烛A的大小、外形完全一样是为了便于比较物像大小关系.

因此拿一支大小和点燃蜡烛相同的蜡烛跟像完全重合,说明像和未点燃的蜡烛完全相同,未点燃的蜡烛和点燃的蜡烛相同,这种实验方法叫等效代替法.像和未点燃的蜡烛完全相同,说明平面镜所成的像和物体大小相等.

(3)在实验中用到刻度尺,但尺并不是测量像、物的大小用的,而是测像到镜的距离、物到镜的距离,然后比较二者关系用的.

(4)若移去蜡烛B,并在其所在位置上放一光屏,则光屏上不能接收到蜡烛的像,这说明平面镜成的是虚像.

(5)因为平面镜成像的特点之一是像与物体等大,与物距大小无关,

所以如果把蜡烛A向镜后移动一段距离,又移动蜡烛B去与蜡烛A的像比较,会发现蜡烛A像的大小不变.

故答案为:(1)便于确定像的位置;(2)便于比较物像大小关系;像和物体大小相等;等效替代法;(3)物距与像距;(4)不能;虚;(5)不变.

选择题
阅读理解

Growing up on a tobacco farm, Emma Avery was used to hard times. When she was seven, her family’s farmhouse burned to the ground. Her father made a temporary (临时的) shelter, where eight people had to sleep in two beds. As soon as Emma and her four brothers and two sisters were big enough, they were out in the fields.

Emma would find her comfort in school, even as a C student, thanks to one teacher. When she moved on to middle school, Emma was alarmingly far behind her classmates. She kept her head down, trying not to be noticed, struggling to catch up, and feeling like an outsider.

Then one day, when Emma was 16, a teacher named Mr. Potts changed everything. Looking his students in the eye, Mr. Potts said, "Being a C student does not mean you do not have a valuable contribution to make. Some of you have to work in the fields in the evening and do not have time to study. But if you do your best, you have a gift to give."

The teacher’s words made Emma believe she could do well, and she worked harder. In the end she won a scholarship to St. Paul’s College, graduated with a degree in elementary education in 1967, and got a job in the public-school system. Then, at George Washington University, she received a master’s in education in 1970, and afterwards in the same year she married Ron Smothers.

Over the next six years, Emma taught in public schools in Miami. In 1976, after saving $10,000, she opened her first restaurant in Los Angeles. Eventually Emma stopped teaching, and her business expanded (扩展) to six restaurants.

In gratitude (感激) for what she has been able to achieve, Emma donates a lot. She has no idea how much money she’s given away. She says, "Those I want to help are the C students who just need help, direction and confidence."

小题1:The first paragraph serves to show that Emma ______.

A.was poor and had no time to study

B.was born on a tobacco farm

C.was sad to lose her house

D.was kind enough to help support the family小题2:From the text we learn that Emma ______.

A.won a scholarship to George Washington University

B.was unsuccessful as a businesswoman

C.was thankful to Mr. Potts

D.disliked teaching, and gave up the job小题3:From the second paragraph we can infer that Emma was ______.

A.unintelligent

B.unconfident

C.hard-working

D.Considerate小题4:The text mainly wants to tell us ______.

A.confidence is the first step to success

B.memory of the past is the teacher of the future

C.something attempted, something done

D.nothing is impossible to a willing heart