问题 实验题

实验室现有以下器材:电压为5V的电源、两个量程的电流表、单量程(3V)的电压表、导线、开关和滑动变阻器(规格分别为:“5Ω 0.3A”、“10Ω  0.6A”、“30Ω  0.6A”).请你利用以上器材来测量一个标有“3.5V”小灯泡的功率(小灯泡电阻大约为10Ω).

(1)为了保证电路各元件的安全,你需要选用的滑动变阻器的规格为_______________

(2)如图的实物图缺少三根导线,请你用笔画线代替导线,请将实物图补充完整(导线不能交叉).

(3)将电路连接完整并经检查无误后,闭合开关发现小灯泡发光暗淡、电流表有示数,而电压表无示数,则出现该现象的原因可能是下面的哪一种情况?__________(只填字母序号即可)

A、滑动变阻器某处断路

B、小灯泡处发生断路

C、滑动变阻器被短路

D、电压表的某一个接线柱接触不良

(4)如表是在正确操作情况下所测出的三组实验数据,则小灯泡的额定功率为___________W.

(5)按照教材中实验操作要求,整个电路消耗的电功率最大可以达到___________W.

答案

(1)“10Ω  0.6A”.

(2)

(3)D

(4)1.225

(5)2

阅读理解

Maybe you love them and want to pet every one you see.Or maybe you’re afraid of them and want to move to a dog­free neighborhood.Either way,dogs are a part of life.Millions of people have dogs as pets.You’ll see them all over town,in the city,country,and even when you’re on vacation.

Like many kinds of pets—no matter how small or cute they are—dogs need to be respected as animals that,under certain conditions,could hurt you.Nearly 5 million dog bites happen every year in the United States.No one wants a dog bite,but how do you prevent one?

One dog expert has come up with an easy way for kids to remember some tips to prevent dog bites.It spells “DOG SAFE”.

Don’t tease,please:Teasing a dog can make it angry enough to bite.For instance,if a dog has food or a toy,never try to take it away.You wouldn’t like it if someone took your snack(点心) while you were eating it!

Only pet with permission:Never pet a dog without asking the owner if it’s OK.Some dogs don’t like to be touched by strangers.

Give space:Little kids especially might run right up to a lovely dog and try to pet it or give it a hug.But dogs need space.Crowding a dog can frighten or anger the dog.

Slow down:Some dogs like to chase(追逐) and bite.Of course,you don’t want to be chased or bitten!The way to avoid it is to go slow around dogs.Never run toward them or away from them.If a dog you don’t know runs toward you,freeze.If you need to get away,back up slowly.

Always get help:You may want to bring home a dog that seems lost or injured.But animals who are lost or injured may be very frightened or in pain.Find a grown­up instead who can decide how to care for the animal.

Fingers together:When feeding a dog a treat,put the treat in the palm of your hand and keep your fingers and thumb close together.Why?The dog is less likely to get confused about which is the treat—the doggie snack or your finger!

Even good dogs can bite:Some people are very surprised when their dog bites someone,but all dogs can bite.Avoid doing things that make dogs scared or angry,such as backing them into a corner or bothering them when they are sleeping.

小题1:The purpose of the text is to ________.

A.help kids avoid being bitten by dogs

B.show methods of feeding dogs

C.warn dog owners of danger

D.warn kids to keep away from dogs小题2:You won’t make a dog angry if ________.

A.you let it alone while it is eating

B.you pretend to take its food away

C.you exchange toys with it

D.you play together with it小题3:Which of the following is TRUE according to the text?

A.The owner will be angry if you pet his or her dog.

B.Dogs don’t like to play with people they are familiar with.

C.A dog may rush up to a kid happily when a kid runs straight to it.

D.You can’t pet a dog unless its owner allows you to.小题4:Seeing a dog running after you,you’d better ______.

A.escape quickly

B.hide in a safe place

C.slow down or just stop

D.turn to the owner

单项选择题