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如图所示，电源电动势E=10V，内电阻r=1.0Ω，电阻R1=5.0Ω、R2=8.0Ω、R3=2.0Ω、R4=6.0Ω，R5=4.0Ω，水平放置的平行金属板相距d=2.4cm，原来单刀双掷开关S接b，在两板中心的带电微粒P处于静止状态；现将单刀双掷开关S迅速接到c，带电微粒与金属板相碰后即吸附在金属板上，取g=10m/s2，不计平行板电容器充放电时间，求带电微粒在金属板中的运动时间？

答案

由闭合电路欧姆定律有 I=

E
R+r

而 R=R1+

(R3+R4)R2
R2+R3+R4
=9Ω

代入①式解得  I=1A  

则U1=IR1=5V，U3=

I
2
•R3=1V，U4=
I
2
•R4=3V      

设微粒的质量为m，带电量为q，S接b时微粒P处于静止状态，微粒应带负电，且有mg=q•

U1+U3
d

设S接c时微粒P的加速度为a，在金属板中运动时间为t，则有mg+q•

U4
d
=ma

  

d
2
=
1
2
at2

由②～⑤式代入数据解得  t=0.04s

答：带电微粒在金属板中的运动时间是0.04s．

阅读理解
阅读理解。
         My Favorite Sweater
My favorite sweater grew too small.
I love that sweater best of all.
My grandma made it when I was three.
She made that sweater just for me.

I picked the yarn (毛线), a special blue.
The color of bluebells, wet with dew (露水).
When I was three I was very small.
But now I'm five and much too tall.

I have a new jacket now that's green.
So I gave my sweater to our cat Queen.
Queen just had kittens (小猫) out in the shed.
My favorite sweater is now their bed.
1. What makes the girl think the sweater is her favourite?

[ ]

A. The girl's grandma made it.
B. The girl got it at the age of three.
C. The yarn is the color of bluebells.
D. The cat Queen uses it for the kittens.
2. Why does the girl give the sweater away?

[ ]

A. The girl is tired of the sweater.
B. The girl wants her grandma to make a new sweater.
C. The girl likes her new jacket better than the sweater.
D. The girl thinks the sweater is too small.
3. What will most likely happen to the green jacket?

[ ]

A. The jacket will become too small.
C. The girl will sell the jacket.
B. The kittens will use the jacket for a bed.
D. The jacket will become the girl's favorite.
4. Read this line from the poem: "My favorite sweater grew too small." What does this line mean?

[ ]

A. The girl likes small sweaters.
B. The girl's sweater became smaller than it once was.
C. The girl's grandma made a small sweater.
D. The girl became too big for the sweater.
5. Read this line from the poem: Queen just had kittens out in the shed. The word "shed" in this line
    probably means ______.

[ ]

A. the girl's sweater
B. the girl's jacket
C. the cats' house
D. the cats' sweater
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问答题

某1g含有杂质的氢氧化钠样品溶于水能与5g质量分数为14.6%的盐酸恰好完全反应，计算该样品中氢氧化钠的质量分数．（杂质不与盐酸反应）______．
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