问题 填空题

如图所示,闭合开关S后,向右适当移动滑动变阻器滑片P的过程中,电流表的示数   (选填“变大”、“变小”或“不变”);移动滑片时应注意                                     

答案

变大;干路电流不能超过电流表的量程

题目分析:由电路图可知,灯泡与滑动变阻器串联,电流表测干路电流,根据并联电路独立工作、互不影响可知滑片移动时通过灯泡的电流不变,根据滑片的移动确定接入电路电阻的变化,根据并联电路的电压特点和欧姆定律可知通过滑动变阻器的电流变化,利用并联电路的电流特点可知电流表示数的变化,移动滑片时要注意电流表的示数不能超出其量程.

由电路图可知,灯泡与滑动变阻器串联,电流表测干路电流,

∵并联电路独立工作、互不影响,

∴滑片移动时,通过灯泡的电流不变,

闭合开关S后,向右适当移动滑动变阻器滑片P的过程中,接入电路的电阻变小,

∵并联电路中各支路两端的电压相等,

∴根据欧姆定律可知,通过滑动变阻器的电流变大,

∵并联电路中干路电流等于各支路电流之和,

∴干路电流变大,即电流表的示数变大,移动滑片时应注意干路电流不能超过电流表的量程.

点评:本题考查了并联电路的特点和欧姆定律的应用,分析好滑片移动时对电路的影响是关键,同时要注意电表使用时均不能超过其量程.

阅读理解

Hawaii has planned to be the first U.S. state to roll out(正式推出)electric car stations statewide --- a move towards weaning the islands off oil.

Hawaii, which is far away from the U.S. mainland, imports foreign oil for almost 90 percent of its energy needs. One–third of that oil is used to power cars and buses on island streets. This move will help Hawaii meet its goal of reducing fossil fuel use by 70 percent by 2030.

Better Place, a Palo Alto, California-based company, will build the car recharging stations and provide recharged batteries for electric cars. The company will purchase renewable energy --- such as wind power --- from Hawaiian Electric Co.

Better Place picked Hawaii for the first statewide rollout in part because the islands are a contained environment, with few vehicles (车辆) coming in and out. Better Place would need to build a bigger network across several states to serve some mainland markets. Hawaii also has rich renewable energy resources, including wind, solar and wave power. This is important because Better Place won’t use oil. Better Place plans to recharge its batteries at night with power from Hawaii’s wind farms. That power normally goes unused because of Hawaii’s low nighttime energy needs.

Hawaii is an ideal place to show off Better Place technology because the state welcomes over five million tourists each year from the U.S. mainland, Japan, Canada and the rest of the world. “If we can get them into electric cars when they rent, we do two great things,” Shai Agassi, Better Place’s founder and chief executive officer, said. “One, we avoid emissions (排放物); two, we use the opportunity to educate them, to teach them in Hawaii how it needs to be done in the rest of the world.”

However, Hawaii doesn’t expect to spend any money to improve the network. Maybe it needs to offer tax breaks or other ways to encourage people to buy electric vehicles when they are first offered.

小题1:

The underlined part “weaning the islands off oil” (in Para 1) probably means _________.

A.exploring the islands for oil

B.stopping Hawaii’s dependence on oil gradually

C.importing more oil from other islands

D.increasing the amount of oil used there小题2:

Why is Hawaii chosen to be the first state where car recharging stations will be built statewide? _________

①There are few cars in Hawaii.

②Hawaii can provide environmentally friendly energy.

③Plenty of oil has been found in Hawaii.

④Hawaii is separated from the mainland with few vehicles coming in and out.

A.①, ③

B.②, ③

C.②, ④

D.①, ④小题3:

When visitors to Hawaii rent electric cars, they _________.

A.will be taught it is necessary to do as Hawaiians do to protect the earth

B.will be offered tax breaks

C.need to be told what should be done before travelling

D.should be given the chance to try two things before driving小题4:

We can infer from the passage that _________.

A.Better Place is a company producing electric cars

B.people are not encouraged to buy electric cars

C.electric cars will be recharged with power from renewable resources

D.Hawaii now has reduced the use oil by 90 percent

多项选择题