What is the relationship between the electric and magnetic fields of an electromagnetic wave?
The correct answer is D: They are at right angles. In an electromagnetic wave, the electric field and magnetic field are at right angles (90 degrees) to each other. They are also both perpendicular to the direction of wave propagation.
This is a fundamental property of electromagnetic waves. The electric field and magnetic field oscillate at right angles to each other, and both are perpendicular to the direction the wave is traveling. This creates a three-dimensional wave structure where the E-field, B-field, and propagation direction form three mutually perpendicular axes. This relationship is what makes electromagnetic waves self-propagating - the changing electric field creates the magnetic field, and vice versa.
Exam Tip
E and B fields = Right angles. Remember: In an electromagnetic wave, the electric field and magnetic field are at right angles (90 degrees) to each other, and both are perpendicular to the direction of propagation.
Memory Aid
"**E** and **B** = **E**ach **B**isects (think 'EB = EB' = Each Bisects, at right angles)"
Real-World Application
When you transmit a radio signal, the electromagnetic wave has an electric field and a magnetic field. If the wave is traveling north, the electric field might oscillate east-west, and the magnetic field oscillates up-down. These two fields are at right angles to each other, and both are perpendicular to the northward direction of travel. This is the fundamental structure of all electromagnetic waves, including radio waves.
FCC Part 97.3Key Concepts
Why Other Options Are Wrong
Option A: Incorrect. The electric and magnetic fields travel at the same speed (speed of light). They don't travel at different speeds.
Option B: Incorrect. The fields are not parallel. They are perpendicular (at right angles) to each other.
Option C: Incorrect. The fields don't revolve in opposite directions. They oscillate perpendicular to each other and to the direction of propagation.
题目解析
The correct answer is D: They are at right angles. In an electromagnetic wave, the electric field and magnetic field are at right angles (90 degrees) to each other. They are also both perpendicular to the direction of wave propagation. This is a fundamental property of electromagnetic waves. The electric field and magnetic field oscillate at right angles to each other, and both are perpendicular to the direction the wave is traveling. This creates a three-dimensional wave structure where the E-field, B-field, and propagation direction form three mutually perpendicular axes. This relationship is what makes electromagnetic waves self-propagating - the changing electric field creates the magnetic field, and vice versa.
考试技巧
E and B fields = Right angles. Remember: In an electromagnetic wave, the electric field and magnetic field are at right angles (90 degrees) to each other, and both are perpendicular to the direction of propagation.
记忆口诀
**E** and **B** = **E**ach **B**isects (think 'EB = EB' = Each Bisects, at right angles)
实际应用示例
When you transmit a radio signal, the electromagnetic wave has an electric field and a magnetic field. If the wave is traveling north, the electric field might oscillate east-west, and the magnetic field oscillates up-down. These two fields are at right angles to each other, and both are perpendicular to the northward direction of travel. This is the fundamental structure of all electromagnetic waves, including radio waves.
错误选项分析
Option A: Incorrect. The electric and magnetic fields travel at the same speed (speed of light). They don't travel at different speeds. Option B: Incorrect. The fields are not parallel. They are perpendicular (at right angles) to each other. Option C: Incorrect. The fields don't revolve in opposite directions. They oscillate perpendicular to each other and to the direction of propagation.
知识点
Electromagnetic waves, Electric field, Magnetic field, Right angles
Verified Content
Question from official FCC Technician Class question pool. Explanation reviewed by licensed amateur radio operators.