问题 选择题

穿过某一闭合回路的磁通量Φ随时间t变化的图像分别如下图甲、乙、丙、丁所示,

则下列关于各闭合回路产生的感应电动势的论述,正确的是  (   )

A.图甲中回路产生的感应电动势始终为某一正值

B.图乙中回路产生的感应电动势一直在变大

C.图丙中回路在0~t0时间内产生的感应电动势大于t0~2t0时间内产生的感应电动势

D.图丁中回路产生的感应电动势可能恒定不变

答案

答案:C

题目分析:图甲中因为磁通量不变,所以在线圈中不产生感应电动势,选项A 错误;图乙中磁通量随时间均匀增加,即磁通量的变化率是定值,所以在线圈中会产生恒定的感应电动势,选项B错误;图丙中回路在0~t0时间内直线的斜率大于t0~2t0时间内的直线的斜率,即0~t0时间内磁通量的变化率大于t0~2t0内的磁通量的变化率,所以0~t0时间内产生的感应电动势大于t0~2t0时间内产生的感应电动势,选项C 正确;图丁中曲线的斜率先减小后增大,及产生的感应电动势,先减小后增大,选项D错误。

选择题
阅读理解

阅读理解

     Camels are large animals living in dry areas. There are two species of camels: the Arabian camel

with a single hump from the dry desert, and the Bactrian camel with two humps from Centraland East

Asia. Camels are over 7 feet tall and weigh over 1,600 pounds. They will live up to 40 to 50 years .

Most camels are domesticated(驯化)and fed by people. Camels are plant-eaters.

     Camels are very strong animals with wide, padded feet. They have thick leathery pads on their knees

and chest. Camels have nostrils(鼻孔)that can open and close, protecting them from the desert

environment. Bushy eyebrows and two rows of long eyelashes protect their eyes from sand. Their mouth

is extremely tough, allowing camels to eat thorny(带刺的)desert plants. Their widened feet help them

move without sinking into the sand. Their thick coats reflect sunlight, and also protect them from the

intense heat from desert sand. Their long legs help by keeping them further from the hot ground.

     Camels can go without food and water for 3 to 4 days. They do not store water in their humps as is

commonly believed. The humps are actually a container of fat. Camels are incredibly(难以置信)

well-adapted to their environment. When conditions heat up, camels can increase their own body

temperature, which prevents sweating and therefore water loss. They may not sweat at all during the day.

     Camels are sometimes called "ships of the desert" because people ride them around the hot, dry

deserts of the world. However, the number of camels is becoming smaller for various reasons.

1. According to the passage, camels usually live in           .

A. Asia

B. Africa

C. America

D. Australia

2. Paragraph 2 is mainly about           .

A. camels are useful animals

B. camels are clever animals

C. camels' body structure and function

D. camels' characteristics and habits

3. The reason why camels lose little water in deserts is that they           .

A. get water from green foods

B. can adjust their temperature

C. store enough water in the humps

D. can manage without water

4. What will the author probably talk about following the last paragraph?

A. Ways to protect camels.

B. Habitats of camels.

C. Reasons for raising camels.

D. Functions of camels.