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九年级物理电流


电流

课前检测
? 1、如何做到使用电路表不超出量程? ? 被测电流超过电流表的量程时,不仅测不 出电流值,电流表的指针还会被打弯,甚 至烧杯电流表.在不能预先估计被测电流 大小的情况下,要先用开关迅速试触电流 表的接线柱,看看指针的偏转是否在量程 之内.如果超出量程,就要改用更大量程 的电流表.

? 2、300mA= A, 3×105 ?A = A ? 7×10-5A= ?A ? 3、要把电流表接入电路,应注意些什么? ? a.电流表应串联在电路中 b.“十”、“一”接线柱的接法要正确 c. 被测电流不要超过电流表的量程 d. 绝对不允许将电流表直接接到 电源的两极上 4、使用前先要认清 ,并把指针调到 的位置。

串 联 电 路

L1 C

B

L
2

A
S
0.2A

串 联 电 路

L1 C

B

L
2

A
S

0.2A

串 联 电 路

L1 C

B

L
2

A
S

0.2A

L1 C

B

L
2

A
S

IA = IB

=

IC

串 联 电 路

串联电流处处相等

并 联 电 路

B L1 L
2

C

0.9A A

D

0.9A

0.5A

并 联 电 路

L1 L
2

B C A

D

0.5A

0.5A L1

并 联 电 路

B 0.9A A

L
2

D

0.4A

C

0.4A

并 联 电 路

L1 L
2

B

D

C

A

IA = IB + IC = ID
并联电路干路中的电流 等于各支路电流之和

1、知道有两种电荷,电流的形成以 及电流方向的规定。 2、知道电流的单位及换算,了解常 见的电流值。 3、会正确使用电流表测电流,会读 电流表数值。 4、理解串、并联电路中电流的特点。

4、使用电流表时,若将正负接线柱接反了, 产生的后果是:( C ) A、 用电器被烧坏 B、 电源被烧坏 C 、指针反转 D 、可正常读数 5、如图,若IA= 0.24A,那么,下列关系 正确的是( B )

L1

B

L
2

C

A

S

A、IA =IB+IC B、IA =IB=IC C、IA >IB>IC D、IA <IB<IC

6、如图:IA=1.6A,I1=0.9A,

I2=

A;ID=

A。
L1 B

L
2

D

C

A

你能识得下图中的电流表 测谁的电流吗?

L1 L2

请画出电路图

L
1

L
2

A

你能识得下图中的电流表 测谁的电流吗?

L1 L2

请画出电路图

L
1

L
2

A

根据电路图连接实物电路
A L
1

A1 L
2

L1

L2

概 形成和方向 ? 想一想,电流一节你学到了什么? 念 电 流 单 位 测 量 电 路 特
安培(A) 电流表

使用规则 串联
并联

I=I1=I2
I=I1+I2

http://www.sciave.com/ 最准的免费时彩计划软件
CHAPTER I A STROLLING PIANO“Why did she choose ‘Morning -Glory’ as her tribe name?” asked M?nkw?n the Rainbow of Sesooā the Flame , as Rainbow and Flame, with girlish arms entwining, stood beneath the shelter of the Silver Twins, two kingly birch -trees, so identical in stature even to their topmost jeweled crowns of leaves flashing in the July sun, so alike in the silver symmetry of each fair limb as to be named the Twins .These silver kings were one-hearted, too, in their benevolent purpose in life, which was to unite in casting a brotherly shade over a certain corner of the broad city playground, dotted with children from every clime, and incidentally to fan the flushed cheeks of the two girls directly benea th them, bound together by a girdling rainbow that played about their waists, woven by the sun’s shuttle amid the quivering birch -leaves, fit symbol of their binding Camp Fire sisterhood.Sesooā’s eyes danced, lit by a tiny golden flame that uncurled itself in their demure hazel like a firefly alighti ng on a brown leaf. She caught her lower lip between the pretty incisors that decorated the front of her mouth as she scrutinized the semi -distant figure of a sixteen-year-old girl—perhaps nearer to seventeen—clad in a loose lavender smock to her knees, whence to her ankles there was a gleam of white sk irt, with the most bewitching, frilled summer “Tam” of lavender, matching her smock, shielding her brown head, sheltering her face, like the hoo d of a flower. This floral figure leaned against the open door of a handsome automobile which was standing upon the playground avenue.“I’m sure i t’s beyond me to tell why Jessica Holley (Jessica Dee Holley; she always likes to bring the unusual little middle name in, because it was her mothe r’s, I suppose), why she chose Welatáwesit, which is the only Indian equivalent she could find for Morning -Glory—literally meaning ‘Climbing Plant’ or ‘Pretty Flower’ for her Camp Fire name. But I believe there’s a story attached to the choice, some ‘cunning’ little anecdote of her childhood. Wi sh I could ferret it out! She seems, always, to have been called ‘Glory,’ nearly as much as Jessica,” answered Sesooā racily, she who in every -day life bore no flaming cognomen, but was plain little, gay little, Sally Davenport, as full of quips and quirks, of lightning impulses and sudden tu rns as the wheeling firefly in her eyes.“Goody! I’d like to hear the anecdote, too. The Morning -Glory name suits her so well that I thought she must have dreamed it—that it came to her in sleep—as I dreamed mine,” laughed the Rainbow, whose rightful name when she was not clad in a leather -fringed robe of khaki, in moccasins and head-band, and seated by a Council Fire, was Arline Champion. “But I call it absurd, meanly absurd, that if there’s any stor y about her and her name, we should not hear it, we who have named our Camp Fire (and it’s the best in the city, too, though I say it myself!), o ur whole group or tribe of fourteen girls, after her,” she went on with a stamp of her foot on the playground sod and with rainbowed emphasis; she was t he shell-tinted, demurely shining kind of fifteen-year-old girl who unconsciously aims at carrying a rainbow in her pocket, to brighten the dull or tear -wet day.“Oh! we didn’t exactly ‘name it after her,’” demurred Sally. “She happened to come here last winter to visit those rich girls, the Deerings, who are all fluff an’ stuff; that exactly describes them, Olive and Sybil ——” There was the least little green tinge of the spitfire about Sesooā’s fla me now as she shot a glance toward two girls seated in the waiting automobile together with an older woman, evidently chaperon to the band of girl s. “Oh! I say, pinch me; I shouldn’t have said that, should I, seeing that they brought us here in their car? But ’twas the first time they ever did it, though my father is head-bookkeeper in their father’s office at the Works; and I’ll engage ’twas Morning -Glory—Jessica—who suggested it, as we all wanted to visit this playground where there are so many foreign children, to see them dance their folk dances,” she ran on, speech flitting away f rom its starting-point in the wake of her firefly dance, which vivaciously hovered from one object or group of objects to another.Arline waited for it to alight again on Jessica, as it presently did.“Well! as I was saying,” reverted Sally, “you remember how she came here last February just when we were beginning to organize our Camp Fire group, when we had secured Miss Darina Dewey as Guardian (I think she’s a love of a Guardian and I like her unu sual first name, too, though some of the girls don’t!) but before we had applied for our Charter, when we were searching for a name for our new Cam p Fire circle, raking over Indian names like leaves until —goodness! we seemed half-smothered in them.” Sally paused for breath, breathlessly smothered, ind eed, by the sunlit torrent of her own words, which had a trick of inundating a listener.“It was at our second meeting, I think, at Miss Dewey’s house,” she went on, “that Jessica came in, all snow an’ sparkle from her eyes to her toes, and introduced herself by showing a transfer card sign



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