问题 计算题

如图,xoy平面内的圆o'与y轴相切于坐标原点o。在该圆形区域内,有与y轴平行的匀强电场和垂直于圆面的匀强磁场。一个带电粒子(不计重力)从原点o沿x轴进入场区,恰好做匀速直线运动,穿过场区的时间为T0。若撤去磁场,只保留电场,其他条件不变,该带电粒子穿过场区的时间为T0/2。若撤去电场,只保留磁场,其他条件不变,求:该带电粒子穿过场区的时间。

答案

解:设电场强度为E,磁感强度为B;圆o'的半径为R;粒子的电量为q,质量为m,初速度为v。同时存在电场和磁场时,带电粒子做匀速直线运动,有

只存在电场时,粒子做类平抛运动,有

由以上式子可知x=y=R,粒子从图中的M点离开电场

由以上式子得

只存在磁场时,粒子做匀速圆周运动,从图中N点离开磁场,P为轨迹圆弧的圆心,设半径为r

由以上式子可得

由图

所以,粒子在磁场中运动的时间

阅读理解

阅读理解。

                                             During September: children under 10 years 

                                                    sharing parents room: FREE

● 42 rooms, 33 of which are south facing with a balcony

● Wide range of facilities: safe, mini bar, hair dryer, dressing gowns, direct phone line…

● Heated swimming pool open in summer and winter

● Garages available, free off-street parking

● Ski room, bike room

THE SITUATION

● 250m from the ski-lifts.

● Well located in the center of Chantemerle with its shops, bars, restaurants, ski hire, nightclubs… RATES

● B&B for one week, two people sharing a double room:

● Winter: from 700 euros

● Summer: from 765 euros

● Out of season: from 500 euros

THE RESORT OF SERRE CHEVALIER

● 250 km of pistes for all levels of skier or snowboarder

● A wide range of activities: cross country skiing, snow shoeing, snow park, ice skating, skiing, hot baths…

● An ideal holiday destination all year around GETTING HERE

● The closest airport is Turin, Italy (approx.2 hours) followed by Lyon (2.5 hours).

● Contact us for our minibus transfers.

● Visit the "Getting to Serre Che" page for further information to help you plan your journey.

1. How much would you pay if you stay with your wife and 10-year-old son in a double room in the hotel in

    spring for a week? [ ]

A. From 700 euros

B. From 765 euros

C. more than 500 euros

D. more than 650 euros

2. If you drive to the hotel, you can _____. [ ]

A. only park your car in the garage

B. park you car in the street

C. park your car anywhere in the hotel

D. park your car near the street

3. How long does it take you to go to the hotel from Lyon?[ ]

A. About 2 hours

B. About 2.5 hours

C. About 4.5 hours

D. About 5 hours

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