（1）白炽灯的灯丝断了一截，若搭上仍能使用，则灯丝的电阻将______；
（2）用久的白炽灯发光变暗，原因是灯丝的电阻______；导致通过灯丝的电流______．（填“变大”“变小”或“不变”）
（1）将断了的灯丝再接上，在两段灯丝的接头处，就会有灯丝交叉，交叉点外的灯丝没有接入电路，这样，就使灯丝的长度变短．根据电阻的决定因素，在材料、横截面积都不变的情况下，导体的长度变短，电阻就减小．
（2）用久了的灯丝与新的灯丝相比，灯丝要变细，即横截面积减小，在材料、长度不变的情况下，横截面积越小，导体的电阻越大，由此可知导灯丝的电阻变大．
将其接在原来的电源上，灯丝两端的电压不变，灯丝的电阻增大，根据欧姆定律I=
可知，通过灯丝的电流变小．U R
故答案为：（1）变小
（2）变大；变小
| 完形填空。 | |||
| Hawaii is famous for its beautiful beaches. Every year water sports, especially surfing and water skiing attract 1 tourists to the island. Hawaii has been a magical name to people who like travelling 2 many years. People on 3 sides of the Pacific Ocean (太平洋), in Japan and America, dream of 4 these beautiful islands in the middle of the ocean. In the tropical (热带的) lands, the sun drops like a ball of golden fire into the sea, and it drops so 5 that you can almost see it move. The sun leaves behind a glow (落日余晖) that lights the sky in the quiet water. People often have a quiet, enjoyable time walking along the water. This scenery is not very different from the exciting beauty that greeted the first tourists to these islands centuries ago. They came in canoes(小木筏) not much 6 than small boats. They found the beautiful white sand beaches and the waving palm trees (棕榈树), but there were no grand hotels like 7 we see today. The fist people came to Hawaii nearly 8 years ago. but skyscraper (摩天大楼) hotels were only built in the 25 years. Now aero planes make it possible to fly to Hawaii for the weekend from Tokyo 9 San Francisco. 10 people come from, they really want to appreciate the earliest beauty of Hawaii. They want to see the lovely beaches and the mountains which are almost hidden by the hotels. | |||
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