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A plane electromagnetic wave traveling in the positive direction of an \(x\) axis in vacuum has components \(E_{x}=E_{y}=0\) and \(E_{z}=(2.0 \mathrm{~V} / \mathrm{m}) \cos \left[\left(\pi \times 10^{15} \mathrm{~s}^{-1}\right)(t-x / c)\right] .\) (a) What is the amplitude of the magnetic field component? (b) Parallel to which axis does the magnetic field oscillate? (c) When the electric field component is in the positive direction of the \(z\) axis at a certain point \(P\), what is the direction of the magnetic field component there?

Short Answer

Expert verified
(a) 6.67 x 10鈦烩伖 T; (b) y-axis; (c) Positive y-direction.

Step by step solution

01

Write the Known E-field Amplitude

We are given the electric field component in the z-direction as \[E_z = (2.0 \, \text{V/m}) \cos \left[(\pi \times 10^{15} \, \text{s}^{-1})(t-x/c)\right].\] The amplitude of the electric field is \(E_0 = 2.0 \, \text{V/m}.\)
02

Use Electromagnetic Wave Relations

In a plane electromagnetic wave in a vacuum, the amplitude of the electric field \(E_0\) and the amplitude of the magnetic field \(B_0\) are related by \[c = \dfrac{E_0}{B_0},\] where \(c\) is the speed of light in vacuum (\(c = 3.0 \times 10^8 \, \text{m/s}\)).
03

Solve for Magnetic Field Amplitude

From the relationship we derived in Step 2, solve for \(B_0\):\[B_0 = \dfrac{E_0}{c} = \dfrac{2.0 \, \text{V/m}}{3.0 \times 10^8 \, \text{m/s}} = 6.67 \times 10^{-9} \, \text{T}.\]
04

Determine Magnetic Field Orientation

For an electromagnetic wave traveling in the positive x-direction, the magnetic field is perpendicular to both the electric field and direction of wave propagation. Since the electric field is along the z-axis, the magnetic field must oscillate along the y-axis.
05

Determine Magnetic Field Direction

Use the right-hand rule for electromagnetic waves: point your thumb in the direction of wave propagation (positive x-axis), your fingers in the direction of the electric field (positive z-axis). The palm faces in the direction of the magnetic field, which is the positive or negative y-axis depending on the orientation of the electric field. When \(E_z\) is positive, the magnetic field is in the positive y-direction.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Electric Field Amplitude
The electric field amplitude of an electromagnetic wave is a crucial factor in understanding the wave's intensity. In our given exercise, the amplitude of the electric field is explicitly stated to be 2.0 V/m, represented by the variable \( E_0 \). This value indicates the maximum strength of the electric field, which occurs at the wave's peak. Understanding electric field amplitude is essential because it influences the potency of the electromagnetic wave as it propagates through space. When we describe this electromagnetic wave as a plane wave, it suggests a uniform intensity over the wavefronts, which are perpendicular to the direction of propagation. The given equation for the electric field in the z-direction forms a cosine wave, where the electric field oscillates up and down over time and space with a specific frequency and amplitude. In this case, 2.0 V/m is your peak field strength, showing how powerful the electric field component of the wave is.
Magnetic Field Orientation
Orientation of the magnetic field in an electromagnetic wave is just as important as its amplitude for comprehending the wave's full behavior. Per Maxwell's equations, the electric and magnetic fields in an electromagnetic wave are always perpendicular to each other and to the direction of wave propagation. In the context of the exercise, we know the wave moves along the positive x-axis and the electric field oscillates in the z-direction. This configuration tells us the magnetic field must vibrate along an axis that is perpendicular both to the direction of travel (x-axis) and the electric field's direction (z-axis). Therefore, the magnetic field oscillation occurs along the y-axis. Using the right-hand rule is a helpful technique for figuring out these orientations:
  • Point your thumb in the direction of propagation (positive x-axis).
  • Let your fingers point in the electric field's direction (z-axis).
  • Your palm then pushes in the magnetic field's direction, which will be the y-axis.
This alignment ensures the electric and magnetic fields work together to support the wave's energy transmission without any cancelation.
Plane Wave Propagation
Plane wave propagation is a concept referring to the uniform transmission of electromagnetic waves through space. In the exercise, the electromagnetic wave is specifically defined as a plane wave traveling in the positive x-direction.A plane wave implies that wavefronts are flat and infinite, radiating with consistent phase and amplitude. The wavefronts advance perpendicularly to the direction of travel, carrying energy efficiently from one location to another.In our scenario, this plane wave features:
  • Components with defined electric and magnetic fields that maintain perpendicularity to each other and the x-direction of travel.
  • A uniform structure where both fields oscillate in phase, meaning as the electric field reaches its peak, the magnetic field does the same.
  • The speed of light, \(c = 3.0 \times 10^8 \, \text{m/s}\), guiding the relationship between the electric field amplitude \( E_0 \) and the magnetic field amplitude \( B_0 \) by \[ c = \dfrac{E_0}{B_0} \].
Preserving this relationship is invaluable not just for solving wave-based problems but also for understanding the transmission behaviors of electromagnetic waves across different media.

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Most popular questions from this chapter

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