题目

（17分）如图所示，3条平行导轨MN、CD、EF在同一平面内，MN与CD相距为d1=8.3cm，CD与EF相距为d2=20.0cm，导轨及导体杆电阻忽略不计，M、E间连接电阻R1=10Ω，N、D间连接电阻R­2=20Ω，导体杆ab横跨在3条导轨上，与3条导轨垂直且接触良好，杆的a端到EF的接触点b间的距离l=40.0cm。空间充满匀强磁场，磁感应强度大小B=0.5T，方向如图示。（1）若导体在匀强磁场中匀速向右运动，速度大小v=4.0m/s，求通过电阻R1、R2的电流大小。（2）若导体杆以b为轴，在导轨所在平Are you ready for adventure (冒险)? Then Sunny Shores Sea Camp is the place for you! The activities there are all about the sea.At Sunny Shores Sea Camp, you can get excited and improve your skill-level. You can enjoy the wonders of Sunny Island. From diving（潜水）to sailing, sea science to seafood, Sunny Shores Sea Camp offers courses for your different interest. You can also learn about the sea environments of Sunny Island. It is hard for you to find anywhere else like that.Whether you're a beginner or already an expert (专家), Sunny Shores Sea Camp is a great place that brings together campers from all over the world.Wonderful memories and new friends are waiting for you at Sunny Shores Sea Camp!Camp Activities: Adventure . Sea Biology. Diving . Sailing . Windsurfing Camp Address: Sun Bay , South Florida 000634 Dates: June 28 - July 18 , July 21 -August 9Cost Week: $600 - $900 Campers Ages: From 13 to 17Contact us: Sign up at www.sunnyshoresseacamp.org! Or call 800-645-14231小题1:At Sunny Shores Sea Camp, all the activities are about___________.A．the earthB．foodC．scienceD．the sea小题2:At Sunny Shores Sea Camp, you can___________.A．improve your skill-levelB．learn about sailing storiesC．take19 different coursesD．protect the sea environment小题3:The campers are only___________.A．adults between 18 and 28B．expertsC．teenagers between 13 and 17D．beginners