/*! This file is auto-generated */ .wp-block-button__link{color:#fff;background-color:#32373c;border-radius:9999px;box-shadow:none;text-decoration:none;padding:calc(.667em + 2px) calc(1.333em + 2px);font-size:1.125em}.wp-block-file__button{background:#32373c;color:#fff;text-decoration:none} Problem 8 An electromagnetic wave of wavel... [FREE SOLUTION] | 91Ó°ÊÓ

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An electromagnetic wave of wavelength \(435 \mathrm{nm}\) is traveling in vacuum in the \(-z\) -direction. The electric field has amplitude \(2.70 \times 10^{-3} \mathrm{~V} / \mathrm{m}\) and is parallel to the \(x\) -axis. What are (a) the frequency and (b) the magnetic-field amplitude? (c) Write the vector equations for \(\overrightarrow{\boldsymbol{E}}(z, t)\) and \(\overrightarrow{\boldsymbol{B}}(z, t)\)

Short Answer

Expert verified
The frequency of the electromagnetic wave is \(6.90 \times 10^{14} Hz\), the magnetic field amplitude is \(9.0 \times 10^{-12} T\), and the vector equations for \(\overrightarrow{\boldsymbol{E}}(z, t)\) and \(\overrightarrow{\boldsymbol{B}}(z, t)\) are \(\overrightarrow{\boldsymbol{E}}(z, t) = 2.70 \times 10^{-3} \cos\left(\frac{2\pi z}{\lambda} - 2\pi f t\right)\hat{i}\) and \(\overrightarrow{\boldsymbol{B}}(z, t) = 9.0 \times 10^{-12} \cos\left(\frac{2\pi z}{\lambda} - 2\pi f t\right)\hat{j}\)

Step by step solution

01

Calculate Frequency

To find the frequency, use the formula for wave speed, which is \(c=\lambda f\), where \(c\) is the speed of light, \(\lambda\) is the wavelength, and \(f\) is the frequency. Solving for \(f\), we have \(f=c/ \lambda\). Substituting the given values \(c = 3.0 \times 10^8 m/s\), and \(\lambda = 435 nm = 435 \times 10^{-9} m\), we get \(f = (3.0 \times 10^8 m/s) / (435 \times 10^{-9} m) = 6.90 \times 10^{14} Hz\)
02

Calculate Magnetic Field Amplitude

The magnitude of the magnetic field is related to the electric field by the formula \(B = E/c\), where \(E\) is the electric field amplitude, and \(c\) is the speed of light. Substituting the given \(E = 2.70 \times 10^{-3} V/m\) and \(c = 3.0 \times 10^8 m/s\), we get \(B = (2.70 \times 10^{-3} V/m) / (3.0 \times 10^{8} m/s) = 9.0 \times 10^{-12} T\) where \(T\) is Tesla, the unit for the magnetic field
03

Write Vector Equations

The electric field \(\overrightarrow{\boldsymbol{E}}(z, t)\) can be expressed in general form as \(\overrightarrow{\boldsymbol{E}}(z,t) = E_0\cos(kz-wt + \phi)\hat{i}\) where \(\hat{i}\) is the unit vector in the x direction and the wave travels in the -z direction with a phase constant \(\phi\) of 0 here. Substituting \(E_0 = E = 2.70 \times 10^{-3} V/m\), \(k = 2\pi/\lambda\), \(f = 6.90 \times 10^{14} Hz\)(which gives the angular frequency \(w = 2\pi f\)), we get \(\overrightarrow{\boldsymbol{E}}(z, t) = 2.70 \times 10^{-3} \cos\left(\frac{2\pi z}{\lambda} - 2\pi f t\right)\hat{i}\). The magnetic field \(\overrightarrow{\boldsymbol{B}}(z, t)\) can be represented similarly as \(\overrightarrow{\boldsymbol{B}}(z,t) = B_0\cos(kz-wt + \phi)\hat{j}\) where \(B_0 = B = 9.0 \times 10^{-12}T\) and \(\hat{j}\) is the unit vector in the y direction.

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Key Concepts

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

Wavelength
Wavelength is a fundamental property of electromagnetic waves and represents the distance between two consecutive peaks or troughs. It's usually denoted by the Greek letter \(\lambda\). In our exercise, the electromagnetic wave has a wavelength of \(435\, \text{nm}\), which can be converted to meters (\(435 \times 10^{-9}\, \text{m}\)) for calculations in physics. Understanding wavelength helps us identify not only the type of wave (like visible light or radio waves) but also its energy and behavior in different media. Wavelength is inversely proportional to frequency; as one increases, the other decreases.
Frequency
Frequency, denoted by \(f\), is the number of wave cycles that pass a point in one second, measured in Hertz (Hz). For electromagnetic waves, it can be calculated using the formula \(f = c / \lambda\), where \(c\) is the speed of light \( (3.0 \times 10^8\, \text{m/s}) \). In the given exercise, substituting the wavelength, we calculate the frequency as \(6.90 \times 10^{14}\, \text{Hz}\). This frequency falls in the visible light range. Knowing frequency helps in understanding how electromagnetic waves interact with matter, and it's crucial for practical applications like communication and radar systems.
Electric Field
The electric field, represented by \(\overrightarrow{\boldsymbol{E}}\), is a vector field associated with electromagnetic waves that describes the electric force a charge would experience at any point in space. In our scenario, the electric field has an amplitude of \(2.70 \times 10^{-3}\, \text{V/m}\) and lies parallel to the \(x\)-axis, meaning it oscillates in that direction as it travels. The strength of the electric field determines how much energy the wave carries. It's described by the equation \( \overrightarrow{\boldsymbol{E}}(z, t) = E_0\cos(kz - \omega t)\hat{i}\), where \(E_0\) is the field's peak value, and \(\hat{i}\) indicates direction.
Magnetic Field
The magnetic field, denoted by \(\overrightarrow{\boldsymbol{B}}\), is another vector field component of electromagnetic waves, which works perpendicularly to the electric field and the direction of wave propagation. Its amplitude can be discovered using \(B = E/c\), where \(E\) is the electric field amplitude and \(c\) is the speed of light. In the exercise, this results in \(9.0 \times 10^{-12}\, \text{T}\), which is quite small but significant in the electromagnetic spectrum. It oscillates perpendicular to the electric field, usually in the \(y\)-axis when the electric field is in the \(x\)-axis, and it plays a vital role in how electromagnetic waves transfer energy.

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Most popular questions from this chapter

The energy flow to the earth from sunlight is about \(1.4 \mathrm{~kW} / \mathrm{m}^{2}\). (a) Find the maximum values of the electric and magnetic fields for a sinusoidal wave of this intensity. (b) The distance from the earth to the sun is about \(1.5 \times 10^{11} \mathrm{~m} .\) Find the total power radiated by 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 microwaves in a certain microwave oven have a wavelength of \(12.2 \mathrm{~cm} .\) (a) How wide must this oven be so that it will contain five antinodal planes of the electric field along its width in the standing-wave pattern? (b) What is the frequency of these microwaves? (c) Suppose a manufacturing error occurred and the oven was made \(5.0 \mathrm{~cm}\) longer than specified in part (a). In this case, what would have to be the frequency of the microwaves for there still to be five antinodal planes of the electric field along the width of the oven?

Radio station WCCO in Minneapolis broadcasts at a frequency of \(830 \mathrm{kHz}\). At a point some distance from the transmitter, the magnetic- field amplitude of the electromagnetic wave from \(\mathrm{WCCO}\) is \(4.82 \times 10^{-11} \mathrm{~T}\). Calculate (a) the wavelength; (b) the wave number; (c) the angular frequency; (d) the electric-field amplitude.

A space probe \(2.0 \times 10^{10} \mathrm{~m}\) from a star measures the total intensity of electromagnetic radiation from the star to be \(5.0 \times 10^{3} \mathrm{~W} / \mathrm{m}^{2}\). If the star radiates uniformly in all directions, what is its total average power output?

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