当导体两端的电压是4V时，导体中的电流是0.5A，如果电压变为3V，导体中的电流为多少？如果通过导体的电流为2A，则导体两端的电压为多少？
∵I=
，U R
∴导体电阻R=
=U I
=8Ω；4V 0.5A
当电压是3V时，通过导体的电流：
I′=
=U′ R
=0.375A；3V 8Ω
∵I=
，U R
∴导体两端电压U″=I″R=2A×8Ω=16V；
答：如果电压变为3V，导体中的电流为0.375A；
如果通过导体的电流为2A，则导体两端的电压为16V．
完形填空(共20小题; 每小题1.5分，满分30分) 阅读短文, 掌握大意, 然后从各题所给的A、B、C、D四个选项中, 选出一个最佳答案，并在答题卡将该项涂黑。 For Chinese students, the end of their senior year is filled with studying and 36 when they prepare for the college entrance exams in June. But for American high school seniors, the experience 37 be more different. It is a celebration of their time in high school and 38 parties, games and fun. Seniorities is a commonly used 39 . It means seniors have a disease which 40 them unable to do work. This starts in April, 41 seniors find out whether they have been accepted to university. Unwilling to do school work, seniors have plenty of 42 activities to focus on. Many school have a “Senior Show”. Only seniors are allowed to perform in it. Some seniors sing 43 dance but many of them perform skits (滑稽短剧).They 44 their favorite teachers or their friends. For example, a group of boys may 45 and imitate a group of their friends. It is all 46 . The “Senior Show” is just a part of Senior Week — the week 47 intended for seniors. During this week, seniors usually get academic or athletic 48 for their wonderful jobs in high school. They also vote 49 one of their male and female classmates who they believe 50 the best-looking or funniest or most involved, etc. These are then 51 in the yearbook. The yearbook is an important part of high school for seniors. There are all their pictures and some words from them in it. Seniors will 52 to get 53 signed by their friends so they can always remember their time together. The end of 54 is a truly special and wonderful time for American students. It’s 55 they will remember for the rest of their lives.
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