Name: electromagnetic wave reflection at conductors
Uploaded: 2023-09-18T17:11:17.000Z
Duration: 1 min 15 s
Channel: JoVE

K12 Standards

Virginia  Standards of Learning

HIgh School

Physical Science

PS.7

PS.7.a

Standing Electromagnetic Waves

تذكر الموجات الدائمة التي تشكلت في خيط ضيق. 
الموجات الدائمة هي مزيج من موجتين تتحركان في الاتجاه المعاكس ولكن لهما نفس السعة والتردد.
ضع في اعتبارك ورقة موصلة مثالية موضوعة في المستوى yz. تضرب الموجة الكهرومغناطيسية المستقطبة خطيا الورقة ، أثناء انتقالها في الاتجاه السالب x.
تحفز الموجة الساقطة التيار على سطح الموصل ، مما ينتج عنه مجالات كهربائية إضافية ، مما ينتج عنه موجة منعكسة بنفس التردد والسعة مثل الموجة الساقطة.
يولد تراكب هاتين الموجتين الموجة الدائمة. تبسيط هذه التعبيرات يوفر النقاط الموجودة على الموجة حيث تكون مقادير المجال الكهربائي والمجال المغناطيسي صفرا. وتسمى هذه العقد أو الطائرات العقدية.
العقدة المضادة هي نقطة ينتقل فيها السعة من الحد الأقصى الموجب إلى الحد الأقصى للإزاحة السلبية.
تتزامن عقد المجال الكهربائي مع العقد المضادة للمجالات المغناطيسية ، والعكس صحيح. وبالتالي ، فهي خارج الطور بزاوية 90 درجة في كل نقطة.

<ol>
	<li>يونغ ، إتش دي وفريدمان ، ر. (2012). الفيزياء الجامعية مع الفيزياء الحديثة. سان فرانسيسكو ، كاليفورنيا: بيرسون. القسم 32.5; الصفحات 1069-1070.</li>
</ol>

الموجات الكهرومغناطيسية الدائمة

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 يمكن انعكاس الموجات الكهرومغناطيسية؛ يمكن أن يكون سطح الموصل أو العازل بمثابة عاكس. كما تخضع المجالات الكهربائية والمغناطيسية لمبدأ التراكب، كذلك الموجات الكهرومغناطيسية. يؤدي تراكب الموجة الساقطة والموجة الكهرومغناطيسية المنعكسة إلى إنتاج موجة ثابتة مماثلة للموجات الدائمة التي تنشأ على وتر مشدود.

 لنفترض أنه تم وضع شريحة من موصل مثالي في المستوى yz، وضربتها موجة كهرومغناطيسية مستقطبة خطيًا تنتقل في الاتجاه x السالب. بما أن المجال الكهربائي لا يمكن أن يحتوي على مكون موازي لسطح موصل مثالي، فيجب أن يكون المجال الكهربائي صفرًا في كل مكان في المستوى yz. المجال الكهربائي للموجة الكهرومغناطيسية الساقطة ليس صفرًا في جميع الأوقات في المستوى yz، لكن هذه الموجة الساقطة تحرض تيارات متذبذبة على سطح الموصل، مما يؤدي إلى ظهور مجال كهربائي إضافي . إن المجال الكهربائي الصافي، وهو المجموع المتجهي لهذا المجال والمجال الساقط، يساوي صفرًا في كل مكان داخل الموصل وعلى سطحه. تنتج التيارات المستحثة على سطح الموصل أيضًا موجة منعكسة تنتقل من المستوى. ينص مبدأ التراكب على أن المجال الإجمالي عند أي نقطة هو المجموع المتجهي للمجالات الكهربائية للموجات الحادثة والمنعكسة، على غرار المجال المغناطيسي. يؤدي تراكب الموجات الساقطة والمنعكسة إلى توليد موجات واقفة.


 <img alt="Equation1" src="/files/ftp_upload/13829/13829_Equation_1.png" style="text-align: center; height: 24px;">

 <img alt="Equation2" src="/files/ftp_upload/13829/13829_Equation_2.png" style="text-align: center; height: 22px;">

 يوفر تبسيط هذه التعبيرات النقاط على الموجة التي يكون فيها المجال الكهربائي والمجال المغناطيسي صفرًا. وتسمى هذه العقد أو الطائرات العقدية. في منتصف المسافة بين أي مستويين عقديين متجاورين توجد الطائرات ذات السعة القصوى؛ هذه هي المستويات المضادة للعقد.


 المجال الكهربائي الإجمالي هو دالة جيب التمام، والمجال المغناطيسي الإجمالي هو دالة جيب التمام. ولذلك، فإن الاختلافات الجيبية للمجالين تكون خارج الطور عند كل نقطة. تتطابق عقد المجال الكهربائي مع نقيض المجالات المغناطيسية والعكس صحيح. وبالتالي، فهي 90&#176؛ خارج المرحلة في كل نقطة. وهذا على النقيض من موجة تنتقل في اتجاه واحد، حيث تكون الاختلافات الجيبية للمجالين الكهربائي والمغناطيسي في الطور عند أي نقطة معينة.


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يمكن أن تنعكس الموجات الكهرومغناطيسية. يمكن أن يعمل سطح الموصل أو العازل الكهربائي كعاكس. كما تطيع المجالات الكهربائية والمغناطيسية ...

Education

JoVE Core

Physics

الفيزياء

Unit 1

الوحدة الأولى

Electromagnetic Waves

الموجات الكهرومغناطيسية

KEY TERMS AND CONCEPTS

المصطلحات والمفاهيم الأساسية

electromagnetic wave reflection at conductors

Electromagnetic waves can reflect from a conductor or a dielectric. When the reflected wave combines with the incoming wave, the result is a standing electromagnetic wave. This is similar to the standing waves formed on a stretched string.

To see how this happens, consider a perfect conductor placed in the yz-plane. A linearly polarized electromagnetic wave moving in the negative x-direction strikes the surface. The electric field cannot have a component parallel to the surface of a perfect conductor, so the electric field must be zero everywhere in the yz-plane.

The incident wave is not zero at the surface, but it induces oscillating currents on the conductor. These currents create an additional electric field. The net electric field is the vector sum of the incident and induced fields, and it is zero everywhere inside and on the conductor's surface. The same surface currents also produce a reflected wave that moves away from the plane.

The total field at any point is the vector sum of the incident and reflected electric fields, and the same idea applies to the magnetic field. This superposition creates standing waves. The places where the electric or magnetic field magnitude is zero are called nodes, or nodal planes. The planes halfway between adjacent nodes have maximum amplitude and are called antinodal planes.

For these standing waves, the total electric field follows a sine function, while the total magnetic field follows a cosine function. The two fields are therefore 90° out of phase at each point. Electric field nodes line up with magnetic field antinodes, and magnetic field nodes line up with electric field antinodes. This is different from a wave traveling in one direction, where the electric and magnetic fields are in phase at a given point.

Electromagnetic Wave Reflection at Conductors

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key terms and concepts

Explore how reflected electromagnetic waves form standing patterns at conductors, with nodes, antinodes, and electric and magnetic fields out of phase.

Electromagnetic Wave Reflection at Conductors | JoVE K12

physics

JoVE Core Physics introduces the theory and application of fundamental physics topics, including kinematics, dynamics, fluid mechanics, statics, waves, and acoustics, with concise and easy-to-understand animated videos. Additionally, the scientist-in-action videos demonstrate the application of related concepts in classical and original research experiments performed in today's laboratories worldwide.

Minnesota Academic Standards in Science

9-12

4.2.1 9P.3.2.2.1

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New Jersey Student Learning Standards for Science

High School

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HS-PS4-5

Alabama Course of Study Science

9-12.PS.2.2.e

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Florida Department of Education

SC.912.P.10

SC.912.P.10.17

south-carolina-college-and-career-ready-science-standards

South Carolina College and Career Ready Science Standards

P-PS4-2

P-PS4-4

Earth and Space Science (ESS)

Earth’s Place in the Universe

E-ESS1-2.

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PS.7.b

Electromagnetic Wave Reflection at Conductors

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