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(II) A satellite dish is about \(0.5 \mathrm{~m}\) in diameter. According to the user's manual, the dish has to be pointed in the direction of the satellite, but an error of about \(2^{\circ}\) to either side is allowed without loss of reception. Estimate the wavelength of the electromagnetic waves (speed \(=3 \times 10^{8} \mathrm{~m} / \mathrm{s}\) ) received by the dish.

Short Answer

Expert verified
The estimated wavelength is approximately 14.3 mm.

Step by step solution

01

Convert Degrees to Radians

First, we need to convert the angle from degrees to radians since we'll use it in trigonometric calculations. The error margin is given as \(2^\circ\). We use the conversion \(\frac{\pi}{180}\) to convert degrees to radians: \(2^\circ \times \frac{\pi}{180} \approx 0.0349 \text{ radians}.\)
02

Use Rayleigh's Criterion for Resolution

The smallest resolvable angle by a circular aperture is approximately given by Rayleigh's criterion: \(\theta = 1.22 \frac{\lambda}{D}\), where \(\lambda\) is the wavelength, \(D\) is the diameter of the dish, and the angle \(\theta\) is in radians. Using \(D = 0.5\text{ m}\) and \(\theta = 0.0349\), we need to solve for \(\lambda\).
03

Solve for Wavelength \(\lambda\)

Substitute the known values into Rayleigh's criterion: \(0.0349 = 1.22 \times \frac{\lambda}{0.5}\). Solving for \(\lambda\), we have \(\lambda = \frac{0.0349 \times 0.5}{1.22} \approx 0.0143 \text{ m} = 14.3 \text{ mm}.\)
04

Check for Physical Relevance

Before concluding, confirm that this calculation for wavelength falls within the typical range for satellite communication, which is usually in the microwave range (centimeters to millimeters). The computed wavelength of \(14.3 \text{ mm}\) is appropriate.

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Key Concepts

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

Rayleigh's Criterion
Rayleigh's Criterion is an important concept in optics that helps us determine the ability of an optical system to distinguish between two closely spaced objects. In the context of satellite dish operations, this criterion is utilized to understand how accurately a satellite dish can receive distinct signals without them overlapping or merging into one blurry signal. The criterion states that the smallest angle \( \theta \) at which two points can be resolved is proportional to the wavelength \( \lambda \) of the electromagnetic waves and inversely proportional to the aperture's diameter \( D \). The formula is given by:\[ \theta = 1.22 \frac{\lambda}{D} \]This formula shows that as the diameter \( D \) of the dish increases, or if the wavelength \( \lambda \) decreases, the angular resolution improves, allowing for finer detail. Understanding this can explain why larger dishes can better resolve signals. Always ensure calculations adhere to Rayleigh's Criterion to optimize and accurately direct satellite dishes for the best reception.
Satellite Dish Alignment
Satellite dish alignment is key to ensuring optimal signal clarity and reception. Proper alignment means pointing the dish precisely at the satellite from which you want to receive signals. However, dishes usually allow for a small margin of error to either side, as mentioned in this exercise, where an alignment error of about \(2^{\circ}\) is permissible without losing the reception.Aligning a satellite dish correctly usually involves:
  • Finding the correct azimuth and elevation for your location, often provided by the satellite TV provider.
  • Using tools like a compass, inclinometer, or a satellite finder app to hone in on the satellite's direction.
  • Adjusting the dish while monitoring the signal strength until the best possible reception is achieved.
This process reflects why even small misalignments might not immediately affect reception if the margin of error is small, as in the given \(2^{\circ}\) range. However, for sustained quality, maintaining precise alignment is vital.
Wavelength Calculation
In electromagnetic wave transmission, calculating the wavelength helps understand the signals that satellite dishes receive. In this exercise, we are asked to compute the wavelength of the signals directed at the dish. The formula connects the dish diameter, resolution angle, and wavelength, derived from Rayleigh's criterion:\[ \lambda = \frac{\theta \times D}{1.22} \]Given the diameter \( D = 0.5 \text{ m} \) and an allowable misalignment angle of \( \theta = 0.0349 \) radians, substituting into the formula gives us:\[ \lambda = \frac{0.0349 \times 0.5}{1.22} \approx 0.0143 \text{ m} \]This result of approximately \(14.3 \text{ mm}\) is typical for satellite communications, which often use microwaves. Calculating wavelength is crucial for ensuring the chosen satellite frequency aligns with the dish's design, optimizing signal reception without unnecessary interference.

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Most popular questions from this chapter

(1) Suppose at \(t=0,\) a wave shape is represented by \(D=A \sin (2 \pi x / \lambda+\phi) ;\) that is, it differs from Eq. 9 by a constant phase factor \(\phi .\) What then will be the equation for a wave traveling to the left along the \(x\) axis as a function of \(x\) and \(t ?\)

(II) The displacement of a standing wave on a string is given by \(D=2.4 \sin (0.60 x) \cos (42 t),\) where \(x\) and \(D\) are in centimeters and \(t\) is in seconds. (a) What is the distance (cm) between nodes? (b) Give the amplitude, frequency, and speed of each of the component waves. (c) Find the speed of a particle of the string at \(x=3.20 \mathrm{~cm}\) when \(t=2.5 \mathrm{~s}\).

(II) Dimensional analysis. Waves on the surface of the ocean do not depend significantly on the properties of water such as density or surface tension. The primary "return force" for water piled up in the wave crests is due to the gravitational attraction of the Earth. Thus the speed \(v(\mathrm{m} / \mathrm{s})\) of ocean waves depends on the acceleration due to gravity \(g .\) It is reasonable to expect that \(v\) might also depend on water depth \(h\) and the wave's wavelength \(\lambda\) . Assume the wave speed is given by the functional form \(v=C g^{\alpha} h^{\beta} \lambda^{\gamma},\) where \(\alpha, \beta, \gamma,\) and \(C\) are numbers without dimension. \((a)\) In deep water, the water deep below does not affect the motion of waves at the surface. Thus \(v\) should be independent of depth \(h\) (i.e., \(\beta=0 ) .\) Using only dimensional analysis, determine the formula for the speed of surface waves in deep water. \((b)\) In shallow water, the speed of surface waves is found experimentally to be independent of the wavelength (i.e., \(\gamma=0 ) .\) Using only dimensional analysis, determine the formula for the speed of waves in shallow water.

(II) Show that the frequency of standing waves on a cord of length \(\ell\) and linear density \(\mu\), which is stretched to a tension \(F_{\mathrm{T}},\) is given by $$f=\frac{n}{2 \ell} \sqrt{\frac{F_{\mathrm{T}}}{\mu}}$$ where \(n\) is an integer.

(II) A cord of length \(1.0 \mathrm{~m}\) has two equal-length sections with linear densities of \(0.50 \mathrm{~kg} / \mathrm{m}\) and \(1.00 \mathrm{~kg} / \mathrm{m}\). The tension in the entire cord is constant. The ends of the cord are oscillated so that a standing wave is set up in the cord with a single node where the two sections meet. What is the ratio of the oscillatory frequencies?

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