问题 选择题

—I really apologize for not being able to join in your birthday party.

—_______. We'll get together later.[ ]

A. Go ahead

B. Not to worry

C. That's right

D. Don't mention it

答案

答案:D

问答题

利用霍尔效应制作的霍尔元件以及传感器,广泛应用于测量和自动控制等领域.

如图1,将一金属或半导体薄片垂直置于磁场B中,在薄片的两个侧面a、b间通以电流I时,另外两侧c、f间产生电势差,这一现象称为霍尔效应.其原因是薄片中的移动电荷受洛伦兹力的作用向一侧偏转和积累,于是c、f间建立起电场EH,同时产生霍尔电势差UH.当电荷所受的电场力与洛伦兹力处处相等时,EH和UH达到稳定值,UH的大小与I和B以及霍尔元件厚度d之间满足关系式UH=RH

IB
d
,其中比例系数RH称为霍尔系数,仅与材料性质有关.

(1)设半导体薄片的宽度(c、f间距)为l,请写出UH和EH的关系式;若半导体材料是电子导电的,请判断图1中c、f哪端的电势高;

(2)已知半导体薄片内单位体积中导电的电子数为n,电子的电荷量为e,请导出霍尔系数RH的表达式.(通过横截面积S的电流I=nevS,其中v是导电电子定向移动的平均速率);

(3)图2是霍尔测速仪的示意图,将非磁性圆盘固定在转轴上,圆盘的周边等距离地嵌装着m个永磁体,相邻永磁体的极性相反.霍尔元件置于被测圆盘的边缘附近.当圆盘匀速转动时,霍尔元件输出的电压脉冲信号图象如图3所示.

a.若在时间t内,霍尔元件输出的脉冲数目为P,请导出圆盘转速N的表达式.

b.利用霍尔测速仪可以测量汽车行驶的里程.除此之外,请你展开“智慧的翅膀”,提出另一个实例或设想.

阅读理解

阅读理解。

     Transport Guide

     The Brisbane City Council(BCC)is responsible for bus and ferry services within the city limits and

suburbs, Most buses will either arrive at the city or an interchange where connecting buses can be caught. BCC buses operate from 5:30 am to 11:00 pm Monday to Thursday and 5:30 am to 12:00 am on

Fridays. On weekends and public holidays buses operate less frequently. Prepaid bus tickets can be

purchased from the QUT (Queensland University of Technology)bookshop, the campus newsagency

most other newsagencies and general stores, and any BCC Customer Service Centre. Shortterm

students at QUT cannot use their ID cards to gain a discount fare on BCC public transport. You will

need to buy an adult ticket to travel. Bus fares are dependent on the number of zones you have to travel.

There are several types of tickets:

     Single : one way ticket to reach your destination, including transfers within 2 hours.

     Daily: unlimited travel within the zones.

     Offpeak Daily: discounted unlimited travel between 9:00 am and 3:30 pm and after 7:00 pm

     Monday to Friday, and all day on weekends and public holidays.

     Weekly: unlimited travel within the zones for one week from the date of issue. Monthly: unlimited

travel within the zones for one calendar month from the date of issue.

     Tentrip Saver: 10 trips at any time within the zones on buses and ferries only.

     Transport routes, timetables and fare information are available from:

     Public Transport Information Centre

     69 Ann Street (corner of George St)

     Brisbane City

     Phone 13 12 30(Transport Information Service)

1. The transport guide above is most likely provided by________.

A. Public Transport Information Centre

B. the Brisbane City Council

C. Queensland University of Technology.

D. BCC Customer Service Centres

2.We can learn from the passage that________.

A. buses are scheduled as usual on weekends and public holidays

B. regular students at QUT need to buy adult tickets

C. prepaid tickets can be bought from the Public Transport Information Centre

D. Tentrip Savers can be used at offpeak time

3. An exchange student staying at QUT for five days has to travel between zones every day.

   What type of ticket would he probably buy?

A. Single.  

B. Weekly.

C. Offpeak Daily.  

D. Tentrip Saver.