Section outline

  • General

    Collapse all Expand all

  • 微波微波

    A person holds a radar gun while a child practices pitching a baseball.

    This person is pointing a gun at a kid practicing his baseball pitch . But it’s not the type of gun that can be used as a weapon. It’s a radar gun, and it’s used to detect the of moving objects. It has measured this pitch to be going at 51 miles per hour. Do you know how a radar gun works? Instead of shooting bullets, it “shoots” .
    ::这个人用枪指着一个练习棒球的小孩。 但这不是可以用作武器的那种枪。 这是一支雷达枪,用来探测移动物体。 它测量这个球速是每小时51英里。 你知道雷达枪是如何工作的吗? 它不是射子弹,而是“射击 ” 。

    Defining Electromagnetic Waves
    ::电磁波的定义

    Electromagnetic waves carry through matter or space as vibrating electric and magnetic fields. Electromagnetic waves have a wide range of and frequencies. The complete range is called the . The Figure shows all the waves of the spectrum. The waves used in radar guns are microwaves.
    ::电磁波作为振动电磁场,在物质或空间中携带电磁波。电磁波具有广泛的频率和频率。整个射程称为.图显示频谱的所有波。雷达枪中使用的波是微波。

    Electromagnetic spectrum showing various waves, their wavelengths, and related scales.

    Defining Microwaves
    ::界定微波

    Find the microwave in the Figure . A microwave is an electromagnetic wave with a relatively long wavelength and low frequency. Microwaves are often classified as , but they have higher frequencies than other radio waves. With higher frequencies, they also have more energy. That’s why microwaves are useful for heating food in microwave ovens. Microwaves have other important uses as well, including cell phone transmissions and radar. These uses are described below.
    ::在图中查找微波。微波是一种电磁波,波长相对较长,频率较低。微波通常被归类为(......),但频率高于其他无线电波。由于频率较高,微波的能量也更多。这就是微波对微波炉中食物加热有用的原因。微波还有其他重要用途,包括手机传输和雷达。这些用途将在下文中说明。

    Cell Phones
    ::手机电话

    Cell phone signals are carried through the air as microwaves. You can see how this works in the Figure . A cell phone encodes the sounds of the caller’s voice in microwaves by changing the frequency of the waves. This is called frequency modulation. The encoded microwaves are then sent from the phone through the air to a cell tower. From the cell tower, the waves travel to a switching center. From there they go to another cell tower and from the tower to the receiver of the person being called. The receiver changes the encoded microwaves back to sounds.
    ::手机信号以微波的形式通过空气传递。您可以看到图中如何使用。手机通过改变波的频率,在微波中编码呼叫者的声音。这称为频率调制。然后,加密微波从电话通过空气发送到一个信号塔。从信号塔,波流向一个转换中心。从那里,波流向另一个信号塔,从塔到被调用的人的接收器。接收器将编码微波转换为声音。

    Cell phone communication process: caller, switching center, base stations, and receiver.

    Q: Cell towers reach high above the ground. Why do you think such tall towers are used?
    ::问题:电池塔到达地面高处。你认为为什么使用这样的高塔?

    A: Microwaves can be interrupted by buildings and other obstructions, so cell towers must be placed high above the ground to prevent the interruption of cell phone signals.
    ::A: 建筑物和其他障碍物可以中断微波,因此,电池塔必须放在地面高处,以防止手机信号中断。

    Radar
    ::雷达雷达

    Radar stands for ra dio d etection and r anging. In police radar, a radar gun sends out short bursts of microwaves. The microwaves reflect back from oncoming vehicles and are detected by a receiver in the radar gun. The frequency of the reflected waves is used to compute the speed of the vehicles. Radar is also used for tracking storms, detecting air traffic, and other purposes.
    ::雷达代表无线电探测和测距,在警察雷达中,雷达枪发射短波微波,微波从来回反射,雷达枪的接收器在雷达炮中探测到微波,反波频率用来计算车辆的速度,雷达还用于跟踪风暴、探测空中交通和其他目的。

    Radar gun sending and receiving microwaves from oncoming vehicles.

    Q: How are reflected microwaves used to determine the speed of oncoming cars (see Figure )?
    ::问题:如何使用反射微波来确定行驶汽车的速度(见图)?

    A: As the car approaches the radar gun, the reflected microwaves get bunched up in front of the car. Therefore, the waves the receiver detects have a higher frequency than they would if they were being reflected from a stationary object. The faster the car is moving, the greater the increase in the frequency of the waves. This is an example of the , which can also occur with .
    ::A:当汽车接近雷达枪时,反射微波在汽车前面被聚集起来。因此,接收器探测到的波比固定物体反映的波的频率高。汽车移动越快,波的频率就越高。这是其中的一个例子,也可能发生。

    Summary
    ::摘要

    • Electromagnetic waves vary in their wavelength, frequency, and energy. The full range of electromagnetic waves makes up the electromagnetic spectrum.
      ::电磁波的波长、频率和能量各不相同。电磁波的电磁波构成电磁频谱。
    • Microwaves are electromagnetic waves with relatively long wavelengths and low frequencies. They are used for microwave ovens, cell phones, and radar.
      ::微波是电磁波,波长相对较长,频率较低,用于微波炉、手机和雷达。
    • A cell phone encodes the sounds of the caller’s voice in microwaves by changing the frequency of the waves. The encoded microwaves then travel through the air to a cell tower and eventually to the receiver of the person being called. The receiver decodes the microwaves and changes them back to sounds.
      ::手机通过改变波浪频率,将呼叫者的声音编码为微波。 加密微波随后通过空气传送到一个信号塔,并最终传到被呼叫者的接收器。 接收器解码了微波,并将其转换为声音。
    • Radar stands for radio detection and ranging. It is the use of reflected microwaves to determine vehicle speeds, track storms, or detect air traffic.
      ::雷达代表无线电探测和测距,是使用反射微波来确定车辆速度、跟踪风暴或探测空中交通。

    Review
    ::回顾

    1. What are microwaves?
      ::什么是微波炉?
    2. Identify uses of microwaves.
      ::查明微波的用途。
    3. How does a cell phone use microwaves to encode and transmit sounds?
      ::手机如何使用微波来编码和传送声音?
    4. What does radar stand for? How does radar work?
      ::雷达代表什么 雷达如何运作