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An electromagnetic standing wave in a certain material has frequency \(1.20 \times 10^{10} \mathrm{~Hz}\) and speed of propagation \(2.10 \times\) \(10^{8} \mathrm{~m} / \mathrm{s}\). (a) What is the distance between a nodal plane of \(\overrightarrow{\boldsymbol{B}}\) and the closest antinodal plane of \(\overrightarrow{\boldsymbol{B}}\) ? (b) What is the distance between an antinodal plane of \(\overrightarrow{\boldsymbol{E}}\) and the closest antinodal plane of \(\overrightarrow{\boldsymbol{B}}\) ? (c) What is the distance between a nodal plane of \(\overrightarrow{\boldsymbol{E}}\) and the closest nodal plane of \(\overrightarrow{\boldsymbol{B}}\) ?

Short Answer

Expert verified
All the distances are 4.375 mm.

Step by step solution

01

Determine Wavelength

We start by calculating the wavelength of the electromagnetic wave. The wavelength \( \lambda \) is given by the formula \( \lambda = \frac{v}{f} \), where \( v \) is the speed of the wave and \( f \) is the frequency. Substitute the given values: \[ \lambda = \frac{2.10 \times 10^8 \text{ m/s}}{1.20 \times 10^{10} \text{ Hz}} = 1.75 \times 10^{-2} \text{ m}.\]
02

Distance Between Nodal and Antinodal Planes for \(\overrightarrow{\boldsymbol{B}}\)

For electromagnetic waves, the nodal and antinodal planes for the magnetic field \( \overrightarrow{\boldsymbol{B}} \) are separated by \( \frac{\lambda}{4} \). The distance is \[ \frac{\lambda}{4} = \frac{1.75 \times 10^{-2} \text{ m}}{4} = 4.375 \times 10^{-3} \text{ m}.\]
03

Distance Between Antinodal Planes of \(\overrightarrow{\boldsymbol{E}}\) and \(\overrightarrow{\boldsymbol{B}}\)

The antinodal planes for the electric field \( \overrightarrow{\boldsymbol{E}} \) and magnetic field \( \overrightarrow{\boldsymbol{B}} \) are separated by \( \frac{\lambda}{4} \) as they form standing waves with a phase shift. The calculated distance remains \( 4.375 \times 10^{-3} \text{ m}. \)
04

Distance Between Nodal Planes of \(\overrightarrow{\boldsymbol{E}}\) and \(\overrightarrow{\boldsymbol{B}}\)

Similarly, since the nodal planes for \( \overrightarrow{\boldsymbol{E}} \) and \( \overrightarrow{\boldsymbol{B}} \) are shifted by \( \frac{\lambda}{4} \), the distance between them is also \( 4.375 \times 10^{-3} \text{ m}.\)

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Key Concepts

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

Wavelength Calculation
Calculating the wavelength of electromagnetic standing waves involves a straightforward relation between wave speed, frequency, and wavelength. To find the wavelength \( \lambda \), use the formula \( \lambda = \frac{v}{f} \), where \( v \) is the speed of the wave and \( f \) is its frequency. For this exercise, substituting the given values of speed \( 2.10 \times 10^8 \text{ m/s} \) and frequency \( 1.20 \times 10^{10} \text{ Hz} \) results in a wavelength of \( 1.75 \times 10^{-2} \text{ m} \).

Understanding this calculation is pivotal because the wavelength forms the fundamental basis for determining distances between points of varying wave activity, such as nodes and antinodes. These distances ultimately relate to how the wave behaves in its environment.
Nodal and Antinodal Planes
Nodal and antinodal planes relate to how electromagnetic waves manifest as standing waves. In these waves, nodes are points of zero amplitude, whereas antinodes represent locations of maximum amplitude.

When considering the magnetic field component \( \overrightarrow{\boldsymbol{B}} \) of an electromagnetic wave, the nodal planes and adjacent antinodal planes are separated by a quarter of the wave's wavelength, denoted as \( \frac{\lambda}{4} \). For the given wave, this distance calculates to \( 4.375 \times 10^{-3} \text{ m} \).

This quarter-wavelength spacing is a hallmark of standing wave patterns where the wave reflects back upon itself, creating consistent zones of maximum and minimum intensity. Observe how this regular patterning provides useful information about energy distribution across the wave's progression.
Magnetic Field Wave Behavior
The magnetic field \( \overrightarrow{\boldsymbol{B}} \) in an electromagnetic wave contributes to the overall wave's properties and behaviors. As part of standing waves, the magnetic field oscillates within defined zones. The spacing between nodal and antinodal planes of \( \overrightarrow{\boldsymbol{B}} \) is consistently \( \frac{\lambda}{4} \), showing regular patterning characteristic of standing waves.

Knowing how the magnetic field behaves provides insights into the wave's energy flows and is crucial for applications in technology and scientific research. This spacing also allows for precise calculations and predictions about wave interactions within various mediums or materials.
Electric Field Wave Behavior
The electric field \( \overrightarrow{\boldsymbol{E}} \) shares similar principles of behavior with the magnetic field \( \overrightarrow{\boldsymbol{B}} \), but has specific roles in the wave's dynamics. In electromagnetic standing waves, electric fields too form nodal and antinodal planes, with separations akin to those found in magnetic fields.

Between antinodal planes of \( \overrightarrow{\boldsymbol{E}} \) and \( \overrightarrow{\boldsymbol{B}} \), or nodal planes thereof, the quarter-wavelength spacing \( \frac{\lambda}{4} \) remains consistent. This indicates a phase shift configuration typical in standing waves, ensuring the electric and magnetic components remain out of phase by \( 90^\circ \), preserving the total wave energy and integrity.

In practical terms, understanding electric field behavior helps in elucidating wave-based technologies like antennas and fiber optics, where electric fields guide information transfer effectively.

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Most popular questions from this chapter

A cylindrical conductor with a circular cross section has a radius \(a\) and a resistivity \(\rho\) and carries a constant current \(I\). (a) What are the magnitude and direction of the electric-field vector \(\overrightarrow{\boldsymbol{E}}\) at a point just inside the wire at a distance \(a\) from the axis? (b) What are the magnitude and direction of the magneticfield vector \(\overrightarrow{\boldsymbol{B}}\) at the same point? (c) What are the magnitude and direction of the Poynting vector \(\overrightarrow{\boldsymbol{S}}\) at the same point? (The direction of \(\vec{S}\) is the direction in which electromagnetic energy flows into or out of the conductor.) (d) Use the result in part (c) to find the rate of flow of energy into the volume occupied by a length \(l\) of the conductor. (Hint: Integrate \(\vec{S}\) over the surface of this volume.) Compare your result to the rate of generation of thermal energy in the same volume. Discuss why the energy dissipated in a currentcarrying conductor, due to its resistance, can be thought of as entering through the cylindrical sides of the conductor.

If the eye receives an average intensity greater than \(1.0 \times 10^{2} \mathrm{~W} / \mathrm{m}^{2}\), damage to the retina can occur. This quantity is called the damage threshold of the retina. (a) What is the largest average power (in \(\mathrm{mW}\) ) that a laser beam \(1.5 \mathrm{~mm}\) in diameter can have and still be considered safe to view head-on? (b) What are the maximum values of the electric and magnetic fields for the beam in part (a)? (c) How much energy would the beam in part (a) deliver per second to the retina? (d) Express the damage threshold in \(\mathrm{W} / \mathrm{cm}^{2} .\)

Solar Sail 2. NASA is giving serious consideration to the concept of solar sailing. A solar sailcraft uses a large, lowmass sail and the energy and momentum of sunlight for propulsion. (a) Should the sail be absorbing or reflective? Why? (b) The total power output of the sun is \(3.9 \times 10^{26} \mathrm{~W}\). How large a sail is necessary to propel a \(10,000-\mathrm{kg}\) spacecraft against the gravitational force of the sun? Express your result in square kilometers. (c) Explain why your answer to part (b) is independent of the distance from the sun.

An electromagnetic wave with frequency \(5.70 \times 10^{14} \mathrm{~Hz}\) propagates with a speed of \(2.17 \times 10^{8} \mathrm{~m} / \mathrm{s}\) in a certain piece of glass. Find (a) the wavelength of the wave in the glass; (b) the wavelength of a wave of the same frequency propagating in air; (c) the index of refraction \(n\) of the glass for an electromagnetic wave with this frequency; (d) the dielectric constant for glass at this frequency, assuming that the relative permeability is unity.

The electric field of a sinusoidal electromagnetic wave obeys the equation \(E=(375 \mathrm{~V} / \mathrm{m}) \cos \left[\left(1.99 \times 10^{7} \mathrm{rad} / \mathrm{m}\right) x+\right.\) \(\left.\left(5.97 \times 10^{15} \mathrm{rad} / \mathrm{s}\right) t\right] .\) (a) What are the amplitudes of the electric and magnetic fields of this wave? (b) What are the frequency, wavelength, and period of the wave? Is this light visible to humans? (c) What is the speed of the wave?

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