Concept explainers
(a)
The wave number of the
(b)
The angular frequency of the electromagnetic wave associated with the electric field if the electric field associated with the radio transmissions of a medical helicopter is given by
(c)
The wavelength of the electromagnetic wave associated with the electric field if the electric field associated with the radio transmissions of a medical helicopter is given by
(d)
The frequency of the electromagnetic wave associated with the electric field if the electric field associated with the radio transmissions of a medical helicopter is given by
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COLLEGE PHYSICS
- Suppose the maximum safe intensity of microwaves for human exposure is taken to be 1.00 W/m2. (a) If a radar unit leaks 10.0 W of microwaves (other than those sent by its antenna) uniformly in all directions, how far away must you be to be exposed to an intensity considered to be safe? Assume that the power spreads uniformly over the area of a sphere with no complications from absorption or reflection. (b) What is the maximum electric field strength at the safe intensity? (Note that early radar units leaked more than modern ones do. This caused identi?able health problems, such as cataracts, for people who worked near them.)arrow_forwardRadio waves normally have their E and B fields in specific directions, whereas visible light usually has its E and B fields in random and rapidly changing directions that are perpendicular to each other and to the propagation direction. Can you explain why?arrow_forwardConsider a small, spherical particle of radius r located in space a distance R = 3.75 1011 m from the Sun. Assume the particle has a perfectly absorbing surface and a mass density of = 1.50 g/cm3. Use S = 214 W/m2 as the value of the solar intensity at the location of the particle. Calculate the value of r for which the particle is in equilibrium between the gravitational force and the force exerted by solar radiation.arrow_forward
- CASE STUDY In Example 34.6 (page 1111), we imagined equipping 1950DA, an asteroid on a collision course with the Earth, with a solar sail in hopes of ejecting it from the solar system. We found that the enormous size required for the solar sail makes the plan impossible at this time. Of course, there is no need to eject such an object from the solar system: we only need to change the orbit. A much more pressing problem is Apophis, a 300-m asteroid that may be on a collision course with the Earth and is due to come by on April 13, 2029. It is unlikely to hit the Earth on that pass, but it will return again in 2036. If Apophis passes through a 600-m keyhole on its 2029 pass, it is expected to hit the Earth in 2036. causing great damage. There are plans to deflect Apophis when it comes by in 2029. For example, we could hit it with a 10- to 150-kg impactor accelerated by a solar sail. The impactor is launched from the Earth to start orbiting the Sun in the same direction as the Earth and Apophis. The idea is to use a solar sail to accelerate the impactor so that it reverses direction and collides head-on with Apophis at 8090 km/s and thereby keeps Apophis out of the keyhole. Consider the momentum in the impactors orbit (Fig. P34.75) when the solar sail makes an angle of = 60 with the tangent to its orbit. Current solar sails may be about 40 m on a side, but the hope is to construct some that are about 160 m on a side. Estimate the impactors tangential acceleration when it is about 1 AU from the Sun. Keep in mind that the sail is neither a perfect absorber nor a perfect reflector, and a heavier impactor would presumably be equipped with a larger sail. Dont be surprised by what may seem like a very small acceleration. FIGURE P34.75arrow_forwardCreate Your Own Problem Consider electromagnetic fields produced by high voltage power lines. Construct a problem in which you calculate the intensity of this electromagnetic radiation in W/m2 based on the measured magnetic field strength of the radiation in a home near the power lines. Assume these magnetic field strengths are known to average less than a T. The intensity is small enough that it is difficult to imagine mechanisms for biological damage due to it. Discuss how much energy may be radiating from a section of power line several hundred meters long and compare this to the power likely to he carried by the lines. An idea of how much power this is can be obtained by calculating the approximate current responsible for T fields at distances of tens of meters.arrow_forwardCheck Your Understanding Could a purely electric field propagate as a wave through a vacuum without a magnetic field? Justify your answer.arrow_forward
- Check Your Understanding What conclusions did our analysis of Maxwell's equations lead to about these properties of a plane electromagnetic wave: (a) the relative directions of wave propagation, of the E field, and of B field, (b) the speed of travel of the wave and how the speed depends on frequency, and (c) the relative magnitudes of the E and B fields.arrow_forwardThe maximum magnetic field strength of an electromagnetic field is 5106T. Calculate the maximum electric field strength if the wave is traveling in a medium in which the speed of the wave is 0.75c.arrow_forwardIllustrate that the size of details of an object that can be detected with electromagnetic waves is related to their wavelength, by comparing details observable with two different types (for example, radar and visible light or infrared and X-rays).arrow_forward
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