问题 问答题

如图,长为S=1.0m,宽为L=0.5m的光滑金属框架NMPQ固定于水平面内,并处在磁感应强度大小B=0.4T,方向竖直向下的匀强磁场中,框架的电阻非均匀分布.将质量m=0.1kg,电阻可忽略的金属棒ab放置在框架上,并与框架接触良好.以P为坐标原点,PQ方向为x轴正方向建立坐标.金属棒从坐标原点处以v0=2m/s的初速度,沿x轴正方向做加速度大小为a=2m/s2的匀减速直线运动,运动中金属棒仅受安培力作用.要求:

(1)金属棒ab运动0.5m,框架产生的焦耳热Q;

(2)框架中aMPb部分的电阻R随金属棒ab的位置x变化的函数关系;

(3)金属棒ab沿x轴正方向运动0.5s过程中通过ab的电量q.

答案

(1)通过受力分析得:

金属棒仅受安培力作用,其大小F=ma=0.2N,

金属棒运动0.5m,因为安培力做功量度外界的能量转化成电能

所以框架中产生的焦耳热等于克服安培力做的功,

所以Q=Fs=0.1J.

(2)金属棒所受安培力为F=BIL,

感应电流I=

E
R
=
BLv
R

F=

B2L2v
R
=ma,

由于棒做匀减速运动,根据运动学公式得:v=

v20
-2ax

所以R=0.4

1-x
    (Ω),

(3)框架的电阻是非均匀分布的.q=It,

因为安培力F=BIL=ma,

q=

mat
BL
=0.5C.

答:(1)金属棒ab运动0.5m,框架产生的焦耳热Q是0.1J;

(2)框架中aNPb部分的电阻R随金属棒ab的位置x变化的函数关系是R=0.4 

1-x
    (Ω);

(3)0.5s过程中通过ab的电量q是0.5C.

阅读理解

For travelers with a sense of adventure and who so want to experience some of the history and mystery of the ancient world, here is a list of cool destinations that you may want to consider for your next holiday.

Angkor Wat, Cambodia

Built in the 12th century, Angkor Wat (meaning “capital monastery”) was a temple in the ancient Khmer capital city of Angkor. It is Cambodia’s best-known tourist attraction and appears on the country’s flag. The temple is known for its    beautiful architecture and reliefs. You'll need at least three days to fully discover the delights of the magnificent site.

Machu Picchu, Peru

Machu Picchu was built high in the Andes Mountains of South America by the Inca in the 15th century. Although well preserved its exact purpose is unknown. It is famous throughout the world not only for its incredible design but also for the natural beauty that surrounds it. Give yourself a week to explore this magnificent site and make you’re fit as there will be a lot of climbing.

Stonehenge, England

The entire Stonehenge site was constructed over thousands of years. But why and how it was built remains a mystery. As the weather can be pretty bleak in winter and the crowds huge in summer, we suggest autumn is the best time to visit these monster rocks.

Pompeii, Italy

When Mount Vesuvius erupted in 79 A.D., Pompeii was buried under many layers of ash, preserving the city exactly as it was when the volcano erupted. Because so many objects were preserved, archaeologists and visitors are able to better understand daily life in the ancient Roman Empire.

小题1:Which location offers the most direct view into daily life in the ancient world?

A.Pompeii.

B.Stonehenge.

C.Ankor Wat.

D.Machu Piccu.小题2:Why may people want to visit Machu Piccu?

A.To climb the Andes Mountains.

B.To discover how it was built.

C.To explore both history and nature.

D.To learn to speak Spanish.小题3:When is the best time to visit Stonehenge?

A.Summer.

B.Spring.

C.Winter.

D.Autumn.小题4:Where would you probably read such an article?

A.In a history textbook.

B.In an archeology(考古) journal.

C.In a travel magazine.

D.In an adventure novel.

判断题