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Consider electromagnetic waves propagating in air. (a) Determine the frequency of a wave with a wavelength of (i) \(5.0 \mathrm{~km}\), (ii) \(5.0 \mu \mathrm{m}\), (iii) \(5.0 \mathrm{nm}\). (b) What is the wavelength (in meters and nanometers) of (i) gamma rays of frequency \(6.50 \times 10^{21} \mathrm{~Hz}\) and (ii) an AM station radio wave of frequency \(590 \mathrm{kHz} ?\)

Short Answer

Expert verified
(a) (i) The frequency of a wave with a wavelength of \(5.0 \mathrm{km}\) is \(60 \mathrm{kHz}\). (ii) The frequency of a wave with a wavelength of \(5.0 \mu \mathrm{m}\) is \(60 \mathrm{THz}\). (iii) The frequency of a wave with a wavelength of \(5.0 \mathrm{nm}\) is \(60 \mathrm{PHz}\). \n (b) (i) The wavelength of gamma rays of frequency \(6.5 \times 10^{21} \mathrm{Hz}\) is \(46.2 \mathrm{pm}\) or \(0.0462 \mathrm{nm}\). (ii) The wavelength of an AM station radio wave of frequency \(590 \mathrm{kHz}\) is \(508 \mathrm{m}\) or \(5.08 \times 10^{11}\) nm.

Step by step solution

01

Determine the Frequency of a Wave

Use the formula \(f = c/ \lambda\) where \(c\) is the speed of light and \(\lambda\) is the wavelength. Given that \(c = 3.00 \times 10^8 \mathrm{m/s}\), plug in the wavelength values to calculate the frequency for each case.\n\n(i) For a wavelength of \(5.0 \mathrm{km}\), which equals \(5.0 \times 10^3 \mathrm{m}\).\n(ii) For a wavelength of \(5.0 \mu \mathrm{m} = 5.0 \times 10^{-6} \mathrm{m}\).\n(iii) For a wavelength of \(5.0 \mathrm{ nm} = 5.0 \times 10^{-9} \mathrm{m}\).
02

Determine the Wavelength of a Wave

Now, use the formula \(\lambda = c/f\) to calculate the wavelength. Apply the given frequencies to find the wavelengths in both meters and nanometers. \n(i) For a frequency of \(6.5 \times 10^{21} \mathrm{Hz}\), determine the wavelength in both meters and nanometers (1m = \(10^9\) nm). \n(ii) For an oscillation speed of \(590 \mathrm{kHz} = 590 \times 10^3 \mathrm{Hz}\), determine the wavelength in both meters and nanometers.
03

Compute the Frequencies & Wavelengths

Perform the calculations for each to determine the frequency (for part a) and the wavelength (for part b). This will involve a calculation and a unit conversion.

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Key Concepts

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

Speed of Light
The speed of light, denoted by the symbol 'c', is a fundamental constant of nature that plays a vital role in electromagnetic wave calculations. It is the speed at which all electromagnetic waves propagate in a vacuum, and it has a value of approximately \( 3.00 \times 10^8 \mathrm{m/s} \). This speed is considered to be the universal speed limit, according to Einstein's theory of relativity.

In our everyday context, light seems instantaneous, but in larger scales such as in space, the finite speed dictates how we understand distances and motion. For example, when we observe distant stars, we are looking at the light that left them years ago, seeing into the past thanks to the speed of light. In electromagnetic wave calculations, the speed of light is used to connect the frequency and the wavelength of a wave, a concept that is crucial for understanding how electromagnetic radiation behaves across different media, such as air, water, or vacuum.
Wave Frequency
Frequency, often represented by 'f', is a measure of how often the waves' crests pass a point in a given time interval. It's expressed in Hertz (Hz), where one Hertz equates to one cycle per second.

In terms of electromagnetic waves, the frequency will determine the type of radiation, such as radio waves, microwaves, visible light, ultraviolet, X-rays, or gamma rays - each having a frequency range that defines its position in the electromagnetic spectrum. High-frequency waves, like gamma rays, have much energy and can penetrate through materials which lower frequency waves like radio waves cannot. Understanding wave frequency not only is important for solving physics problems but also for practical applications like tuning your radio to the right station or setting up communication networks.
Wavelength Conversion
Wavelength conversion is the process of translating a wave's length from one unit of measurement to another. This is essential given that wavelengths can vary significantly; radio waves may be meters long, whereas light wavelengths are typically in the nanometer range.

The relationship between speed of light, frequency, and wavelength can be utilized for these conversions. For instance, with the formula \( \lambda = \frac{c}{f} \), when you comprehend the frequency, you can deduce the wavelength in meters, and then convert to any unit like kilometers (\( \mathrm{km} \) ), micrometers (\( \mu\mathrm{m} \) ), or nanometers (\( \mathrm{nm} \)). Conversions and understanding these measurements are not merely academic; they are crucial for areas like fiber-optic communications, astronomy, and any technology relying on the behavior of electromagnetic waves.

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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 \(\vec{E}\) at a point just inside the wire at a distance \(a\) from the axis? (b) What are the magnitude and direction of the magnetic-field vector \(\vec{B}\) at the same point? (c) What are the magnitude and direction of the Poynting vector \(\vec{S}\) 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 current-carrying conductor, due to its resistance, can be thought of as entering through the cylindrical sides of the conductor.

A sinusoidal electromagnetic wave emitted by a mobile phone has a wavelength of \(35.4 \mathrm{~cm}\) and an electric-field amplitude of \(5.40 \times 10^{-2} \mathrm{~V} / \mathrm{m}\) at a distance of \(250 \mathrm{~m}\) from the phone. Calculate (a) the frequency of the wave; (b) the magnetic-field amplitude; (c) the intensity of the wave.

As a physics lab instructor, you conduct an experiment on standing waves of microwaves, similar to the standing waves produced in a microwave oven. A transmitter emits microwaves of frequency \(f .\) The waves are reflected by a flat metal reflector, and a receiver measures the waves' electric-field amplitude as a function of position in the standing-wave pattern that is produced between the transmitter and reflector (Fig. \(\mathbf{P 3 2 . 4 8}\) ). You measure the distance \(d\) between points of maximum amplitude (antinodes) of the electric field as a function of the frequency of the waves emitted by the transmitter. You obtain the data given in the table. $$ \begin{array}{l|llllllllll} f\left(\mathbf{1 0}^{9} \mathbf{H z}\right) & 1.0 & 1.5 & 2.0 & 2.5 & 3.0 & 3.5 & 4.0 & 5.0 & 6.0 & 8.0 \\ \hline d(\mathrm{~cm}) & 15.2 & 9.7 & 7.7 & 5.8 & 5.2 & 4.1 & 3.8 & 3.1 & 2.3 & 1.7 \end{array} $$ Use the data to calculate \(c,\) the speed of the electromagnetic waves in air. Because each measured value has some experimental error, plot the data in such a way that the data points will lie close to a straight line, and use the slope of that straight line to calculate \(c\).

A sinusoidal electromagnetic wave from a radio station passes perpendicularly through an open window that has area \(0.500 \mathrm{~m}^{2}\). At the window, the electric field of the wave has rms value \(0.0400 \mathrm{~V} / \mathrm{m}\). How much energy does this wave carry through the window during a 30.0 s commercial?

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 \(\overrightarrow{\boldsymbol{B}}(z, t)\)

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