Physics for Scientists and Engineers, 6e

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Physics for Scientists and Engineers, 6e. Chapter 34 – Electromagnetic Waves. What is the phase difference between the sinusoidal oscillations of the electric and magnetic fields in this figure? . impossible to determine 180° 90° 0 .

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### Physics for Scientists and Engineers, 6e

Chapter 34 – Electromagnetic Waves

What is the phase difference between the sinusoidal oscillations of the electric and magnetic fields in this figure?
• impossible to determine
• 180°
• 90°
• 0

Figure 34.3b shows that the B and E vectors reach their maximum and minimum values at the same time.

An electromagnetic wave propagates in the –y direction. The electric field at a point in space is momentarily oriented in the +x direction. The magnetic field at that point is momentarily oriented in the

• –x direction
• +y direction
• +z direction
• –z direction

The B field must be in the +z direction in order that the Poynting vector be directed along the –y direction.

Which of the following is constant for a plane electromagnetic wave?
• magnitude of the Poynting vector
• energy density uE
• energy density uB
• wave intensity

The first three choices are instantaneous values and vary in time. The wave intensity is an average over a full cycle.

To maximize the radiation pressure on the sails of a spacecraft using solar sailing, the sheets must be
• very black to absorb as much sunlight as possible
• very shiny, to reflect as much sunlight as possible

To maximize the pressure on the sails, they should be perfectly reflective, so that the pressure is given by Equation 34.27.

If the antenna in the figure represents the source of a distant radio station, rank the following points in terms of the intensity of the radiation, from greatest to least: (1) a distance d to the right of the antenna (2) a distance 2d to the left of the antenna (3) a distance 2d in front of the antenna (out of the page) (4) a distance d above the antenna (toward the top of the page).

• 1, 2, 3
• 2, 4, 1
• 3, 4, 1
• 4, 3, 1

Specifically, (1), (2) = (3), (4). The closest point along the x axis in Figure 34.11 (choice 1) will represent the highest intensity. Choices (2) and (3) correspond to points equidistant in different directions. Choice (4) is along the axis of the antenna and the intensity is zero.

If the antenna in this figure represents the source of a distant radio station, what would be the best orientation for your portable radio antenna, located to the right of the figure?

• up–down along the page
• left–right along the page
• perpendicular to the page

The best orientation is parallel to the transmitting antenna because that is the orientation of the electric field. The electric field moves electrons in the receiving antenna, thus inducing a current that is detected and amplified.

In many kitchens, a microwave oven is used to cook food. The frequency of the microwaves is on the order of 1010 Hz. The wavelengths of these microwaves are on the order of

• kilometers
• meters
• centimeters
• micrometers

Either Equation 34.13 or Figure 34.12 can be used to find the order of magnitude of the wavelengths.

A radio wave of frequency on the order of 105 Hz is used to carry a sound wave with a frequency on the order of 103 Hz. The wavelength of this radio wave is on the order of

• kilometers
• meters
• centimeters
• micrometers

Either Equation 34.13 or Figure 34.12 can be used to find the order of magnitude of the wavelength.