问题 问答题

将长度为2m的导线弯折成等长的两段AB和BC,∠ABC=120°,如图所示,现将它放置在磁感应强度B=1T的匀强磁场中,并使之以v=10m/s的速率在纸面内平动,那么A、C两端可能出现的电势差的绝对值|UAC|的最大值为______V,最小值为______V.

答案

当导体速度方向垂直于AC时,导体中产生的感应电动势最大,E=BLACv=1×

3
×10V=10
3
V
,A、C两端的电势差的绝对值UAC=E=10
3
V

    当导体速度方向沿着AC时,A、C两端电势差的绝对值最小,UAC=0

故本题答案是:10

3
     0

阅读理解

Because earthquakes happen without warning, it’s important to take steps now to prepare. Because you don’t know where you will be when an earthquake happens, prepare some supplies for your home, workplace, and car.

1.Water.

A person need at least 1/2 gallon of water daily just for drinking. Store at least 1 gallon of water per person per day and be prepared for a 72-hour period.It is suggested that you buy bottled water. Keep bottled water in its original container and do not open it until you need to use it. Also, do check the “use by” date.

2.Food.

It’s always a practical idea to keep a supply of nonperishable (不易腐烂的)food on hand. Have an enough supply of canned food, powdered milk, dried fruits, nonsalted nuts and canned juices for at least 72 hours.

3.Flashlights (手电筒) and spare batteries.

Keep a flashlight beside your bed, at your place of work, and in your car. Do not use matches or candles after an earthquake until you are sure that no gas leaks.

Prepare a battery-powered radio and spare batteries. Most telephones will be out of order, so radios will be your best source of information.

4.Clothes.

If you live in a cold place, you must think about warmth. You might not have heat after an earthquake. Think about your clothing and bedding supplies.

小题1:Why should people prepare themselves for an earthquake?

A.Because earthquakes can be known before they happen.

B.Because earthquakes take place without warning.

C.Because earthquakes usually take place in the neighborhood.

D.Because it’s people’s daily work to prepare the earthquakes.小题2:About the prepared water, which description is RIGHT?

A.A person should prepare 0.5 gallon of water for one day.

B.You’d better use your own containers to keep water.

C.You’d better open the bottled water when you buy it.

D.You shouldn’t open the bottled water until you need it.小题3:You should prepare all of the following except ________.

A.powdered milk

B.fresh vegetables

C.dried fruits

D.canned juices小题4:According to the article we know that________.

A.we need to prepare some supplies only at home.

B.a telephone is the most important prepared thing.

C.flashlights but not matches are first used after earthquakes.

D.clothes are used to protect your head.小题5:If you live in a cold place, you should prepare________.

A.some warm clothes and bedding supplies

B.some hot water

C.some batteries

D.some flashlights

单项选择题