问题 计算题

如图所示,在匀强电场中,一电荷量为q=5.0×10-10 C的正电荷,由a点移到b点和由a点移到c点,电场力做的功都是3.0×10-8 J,已知a、b、c三点的连线组成直角三角形,ab=20 cm,θ=37°。求:

(1)a、b两点间的电势差;

(2)匀强电场的场强大小;

(3)电场强度的方向。

答案

解:因为正电荷q从a到b和从a到c,电场力做功相等,所以由W=qU可得Uab=Uac,b、c两点在同一等势面上,则电场强度方向与ac平行,由a指向c

由U=Ed得,

解答题
阅读理解

Imagine that you are sitting in a park and suddenly remember that you need to send an urgent email. You have your laptop computer with you and you connect it to a wireless access point and access the Internet. Then you send your email. This wouldn’t have been possible if there were no wireless Internet for laptops. Wireless Internet has come into our life in so many ways that we don’t even realize what a necessary part it has become of our day-to-day lives.

How do we connect to a wireless Internet service for laptop computers? There are two ways to do this. They are Wi-Fi connection and Bluetooth connection. Wireless networking is very easy. You just switch on the Wi-Fi button that has been provided in the laptop for Wi-Fi scanning. Once that is done, the computer will connect to the Internet.

An interesting fact about Wi-Fi networking is that you can create a network between similar wireless equipment. Consider a situation where you and your friend both have Wi-Fi laptops, and there is some data you want to exchange. Traditional networking architecture demands that you have a wireless router (路由器). But the beauty of Wi-Fi networking technology is that you can set up a network between you and your friend’s laptop, and share all the data you want.

Broadband (宽带) Internet connection is typically preferred by any user as it provides better speed for Internet surfing. Up until the invention of 3G mobile phones, Internet speed on mobile phones was very slow. 3G has the promise of changing the entire face of broadband technology. Just imagine browsing at speeds of more that 2MB per second. To give you a measure of the speed, 3G enables you to watch high quality live videos on the Internet.

It is amazing to see how technology changes and the rate at which it changes. There may come a time when you may be able to browse using mobile wireless Internet for laptops anywhere in the world.

小题1:What can we learn from Paragraph 1?

A.Wireless Internet will become a reality soon.

B.We can send emails outdoors through wireless Internet.

C.Laptops enable us to do business everywhere.

D.People can easily find a laptop to surf the Internet.小题2:People can enjoy a wireless Internet service for laptop computers by      .

A.connecting to another computer

B.switching off the Wi-Fi button

C.using bluetooth connection

D.connecting bluetooth to Wi-Fi小题3:What should we do to share some data with a friend through Wi-Fi networking?

A.Use the same computer.

B.Surf online.

C.Have a wireless router.

D.Set up a network.小题4:One main advantage of 3G mobile phones mentioned in the passage is      .

A.their low price

B.their different functions

C.their high Internet speed

D.their bright future