18.1 电磁波
Section outline
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Did you ever wonder how a microwave works? It directs invisible waves of radiation toward the food placed inside of it. The radiation transfers to the food, causing it to get warmer. The radiation is in the form of , which are a type of electromagnetic waves.
::你有没有想过微波是如何工作的?它将看不见的辐射波引向它体内的食物。辐射向食物转移,使其变暖。辐射以电磁波的形式出现。What Are Electromagnetic Waves?
::什么是电磁波?Electromagnetic waves are waves that consist of vibrating electric and magnetic fields. Like other waves, electromagnetic waves transfer energy from one place to another. The transfer of energy by electromagnetic waves is called electromagnetic radiation . Electromagnetic waves can transfer energy through matter or across empty space.
::电磁波是由振动电磁场和磁场组成的波。 与其他波一样,电磁波将能量从一个地方转移到另一个地方。 电磁波的能量转移被称为电磁辐射。 电磁波可以通过物质或空空空间转移能量。Q: How do microwaves transfer energy inside a microwave oven?
::问题:微波如何在微波炉内转移能量?A: They transfer energy through the air inside the oven to the food.
::A:它们通过烤箱内的空气将能量转移到食物中。May the Force Be With You
::愿生命与你同在A familiar example may help you understand the vibrating electric and magnetic fields that make up electromagnetic waves. Consider a bar , like the one in the Figure . The magnet exerts magnetic force over an area all around it. This area is called a . The field lines in the diagram represent the direction and location of the magnetic force. Because of the field surrounding a magnet, it can exert force on objects without touching them. They just have to be within its magnetic field.
::一个熟悉的例子可能会帮助您理解电磁波构成的振动电磁场。 想象一下一棒, 如图中的一棒。 磁力对周围的区域施加磁力。 这个区域被称为 。 图中的野外线代表磁力的方向和位置。 由于磁力周围的场, 它可以在不触动物体的情况下对物体施压。 它们必须位于磁场之内 。Q: How could you demonstrate that a magnet can exert force on objects without touching them?
::问题:你怎么能够证明磁铁能在不触碰物体的情况下对物体施压?A: You could put small objects containing iron, such as paper clips, near a magnet and show that they move toward the magnet.
::A:你可以把装有铁的小物件,如纸片,放在磁铁附近,显示它们向磁铁移动。An electric field is similar to a magnetic field. It is an area of electrical force surrounding a positively or negatively charged particle. You can see in the following Figure . Like a magnetic field, an electric field can exert force on objects over a without actually touching them.
::电场与磁场相似。它是围绕正或负电荷粒子的电力区域。从下图中可以看到。像磁场一样,电场可以在不实际触碰物体的情况下对物体施压。How an Electromagnetic Wave Begins
::电磁波是如何开始的An electromagnetic wave begins when an electrically charged particle vibrates. The Figure shows how this happens. A vibrating charged particle causes the electric field surrounding it to vibrate as well. A vibrating electric field, in turn, creates a vibrating magnetic field. The two types of vibrating fields combine to create an electromagnetic wave.
::电磁波在电动粒子振动时开始。 图中显示这种情况是如何发生的。 振动充电粒子也导致周围电场振动。 振动电场反过来又产生振动磁场。 两种振动场结合产生电磁波。How an Electromagnetic Wave Travels
::电磁波如何旅行As you can see in the Figure , the electric and magnetic fields that make up an electromagnetic wave are perpendicular (at right angles) to each other. Both fields are also perpendicular to the direction that the wave travels. Therefore, an electromagnetic wave is a . However, unlike a mechanical transverse wave, which can only travel through matter, an electromagnetic transverse wave can travel through empty space. When waves travel through matter, they lose some energy to the matter as they pass through it. But when waves travel through space, no energy is lost. Therefore, electromagnetic waves don’t get weaker as they travel. However, the energy is “diluted” as it travels farther from its source because it spreads out over an ever-larger area.
::从图中可以看到,电磁波的电磁场是垂直的(右角度),两个领域也与波波所穿行的方向相近。因此,电磁波是一个。然而,与机械反向波不同,电磁反向波只能穿梭于物质中,它可以在空空空空间中移动。当波浪穿透物质时,它会失去一些能量。但当波浪穿透空间时,它不会失去能量。因此,电磁波不会随着波浪的移动而变弱。然而,电磁波从源处走得更远,因为它会扩散到越来越广的区域,因此能量是“稀释的 ” 。Electromagnetic Wave Interactions
::电磁波相互作用When electromagnetic waves strike matter, they may interact with it in the same ways that mechanical waves interact with matter. Electromagnetic waves may:
::当电磁波撞击物质时,它们可以与机械波以同样方式与物质相互作用。-
reflect, or bounce back from a surface;
::反射,或从表面反射; -
refract, or bend when entering a new
medium
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::折形,或在进入新介质时弯曲; -
diffract, or spread out around obstacles.
::或散布在障碍物周围。
Electromagnetic waves may also be absorbed by matter and converted to other . Microwaves are a familiar example. When microwaves strike food in a microwave oven, they are absorbed and converted to , which heats the food.
::电磁波也可能被物质吸收并转化成其他物质。 微波是一个常见的例子。 当微波在微波炉中撞击食物时,它们会被吸收并转换成能给食物加热的电磁波。Sources of Electromagnetic Waves
::电磁波源源The most important source of electromagnetic waves on Earth is the sun. Electromagnetic waves travel from the sun to Earth across space and provide virtually all the energy that supports life on our planet. Many other sources of electromagnetic waves depend on technology . , microwaves, and X rays are examples. We use these electromagnetic waves for communications, cooking, medicine, and many other purposes.
::地球电磁波的最重要来源是太阳。电磁波从太阳到地球,横跨空间,提供几乎所有维系地球生命的能量。许多其他电磁波来源都依赖于技术。微波和X光就是例子。我们用这些电磁波进行通信、烹饪、医药和其他许多用途。Launch the Light Wave simulation below to help you visualize light as a transverse wave moving through the electromagnetic field. Be sure to adjust the band slider to observe waves of different sizes, such as Radio Waves and . There is also an illustration of objects of comparable sizes next to the to help you imagine the sizes of these invisible light waves.
::启动下面的光波模拟, 帮助您将光作为横跨电磁场的反向波进行视觉化。 请务必调整带滑动器以观测不同大小的波, 如无线电波 和 。 还有一个类似大小的物体插图, 用来帮助您想象这些看不见的光波的大小 。Further Reading
::继续阅读Summary
::摘要-
Electromagnetic waves are waves that consist of vibrating electric and magnetic fields. They transfer energy through matter or across space. The transfer of energy by electromagnetic waves is called electromagnetic radiation.
::电磁波是由振动电磁场和磁场组成的波,通过物质或跨空间转移能量,电磁波转移能量称为电磁辐射。 -
The electric and magnetic fields of an electromagnetic wave are areas of electric or magnetic force. The fields can exert force over objects at a distance.
::电磁波的电磁场和磁场是具有电力或磁力的地区,可在远处对物体施加威力。 -
An electromagnetic wave begins when an electrically charged particle vibrates. This causes a vibrating electric field, which in turn creates a vibrating magnetic field. The two vibrating fields together form an electromagnetic wave.
::电磁波在电荷粒子振动时开始。这会造成振动电场,从而产生振动磁场。两个振动场共同形成电磁波。 -
An electromagnetic wave is a transverse wave that can travel across space as well as through matter. When it travels through space, it doesn’t lose energy to a medium as a mechanical wave does.
::电磁波是一种横跨空间和穿越物质的横跨波。 当电磁波穿过空间时,它不会像机械波那样失去对介质的能量。 -
When electromagnetic waves strike matter, they may be reflected, refracted, or diffracted. Or they may be absorbed by matter and converted to other forms of energy.
::当电磁波撞击物质发生时,它们可能被反射、反射或分解,或者被物质吸收并转换成其他形式的能量。 -
The most important source of electromagnetic waves on Earth is the sun. Many other sources of electromagnetic waves depend on technology.
::太阳是地球上电磁波的最重要来源,许多其他电磁波来源都依赖于技术。
Review
::回顾-
What is an electromagnetic wave?
::什么是电磁波? -
Define electromagnetic radiation.
::定义电磁辐射。 -
Describe the electric and magnetic fields of an electromagnetic wave.
::描述电磁波的电磁场和磁场。 -
How does an electromagnetic wave begin? How does it travel?
::电磁波是如何开始的? -
Compare and contrast electromagnetic and mechanical transverse waves.
::对比和对比电磁波和机械横跨波。 -
List three sources of electromagnetic waves on Earth.
::列出地球电磁波的三个来源。
Explore More
::探索更多Watch the electromagnetic wave animation and then answer the questions below.
::注意电磁波动画 然后回答下面的问题-
Identify the vibrating electric and magnetic fields of the wave.
::识别波的振动电磁场 -
Describe the direction in which the wave is traveling.
::描述波浪的航行方向。
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reflect, or bounce back from a surface;
