问题 填空题

家庭电路中,三孔插座多的一孔和______相连,防止电器金属外壳漏电.家庭电路中电流过大的原因有:______,保险丝的作用是______.

答案

三脚插头的上面一头和用电器的金属外壳相连,当三脚插头插入三孔插座时,金属外壳和大地相连,人接触漏电的金属外壳用电器时,人被连接大地的导线短路,没有电流从人体通过,不会发生触电事故.

家庭电路中电流过大的原因:短路和总功率过大.

短路时,电阻几乎为零,根据I=

U
R
,电源电压为220V,电阻很小,电流很大.

电路总功率过大时,根据I=

P
U
,电源电压为220V不变,总功率很大,电流很大.

保险丝的作用:当电流增大到一定值时,产生的电热过多,达到保险丝的熔点,自动熔断,保护电路

故答案为:大地;短路和电路总功率过大;当电流增大到一定值时,自动熔断,保护电路.

选择题
阅读理解

Getting close to active or erupting volcanoes can be dangerous. But for Michael Rampino, it’s all in a day’s work. Rampino is a volcanologist, a scientist who studies volcanoes and how they affect our planet. Rampino has been close to red-hot lava flows (熔岩流) in Hawaii and explosive volcanoes in Indonesia. He knows when to get close to an active volcano and when to back away.

Rampino wasn’t always a volcanologist. He worked for NASA for seven years. He studied rocks until he began to research climate change and the effects that volcanoes have on climate. He became interested in the subject. “Once I started working with volcanoes,” Rampino said, “I was hooked.”

Rampino is a professor at New York University. As part of his job, he travels to areas where volcanoes have been active. “Active” means they have erupted within the past few centuries and probably will erupt again. Rampino studies the deposits (沉积物) of ash and other materials from the eruptions. The ash may hold clues to what happened to the Earth in the distant past. It may also help scientists predict what could happen to Earth’s climate in the future.

Rampino doesn’t work alone. He works with a team of scientists who use computers to stimulate (模拟) the effects volcanoes have on Earth’s atmosphere.

Being a volcanologist may be hard work, but it’s also fun. “It’s cool traveling the world studying volcanoes,” Rampino says. When he talks to students about his work, he tells them that his goal is “to understand the events that have shaped Earth’s history.”

小题1:To Rampino, being close to active volcanoes is _____.

A.adventurous but meaningful

B.scary but necessary

C.impossible and unnecessary

D.dangerous but urgent小题2:The underlined word “hooked” in Paragraph 2 probably means “_____”.

A.trapped

B.touched

C.frightened

D.attracted小题3:Rampino’s study on volcanoes might help _____.

A.warn people to protect the environment

B.support the study of Earth’s future climate

C.tell the future eruption time of the volcanoes

D.reduce the possibility of the volcanoes’ eruptions小题4:In which part of a newspaper could we find this text?

A.Climate.

B.History.

C.People.

D.Business.