A LASIK vision correction system uses a laser that emits 10-ns-long pulses of light, each with 2.5 mJ of energy. The laser is focused to a 0.85-mm-diameter circle. a. What is the average power of each laser pulse in units of watts? b. Determine the intensity of the laser light at the focus point. c. What is the electric field amplitude of the laser light at the focus point?

A LASIK vision correction system uses a laser that emits 10-ns-long pulses of light, each with 2.5 mJ of energy. The laser is focused to a 0.85-mm-diameter circle. a. What is the average power of each laser pulse in units of watts? b. Determine the intensity of the laser light at the focus point. c. What is the electric field amplitude of the laser light at the focus point?

Principles of Physics: A Calculus-Based Text

5th Edition

ISBN:9781133104261

Author:Raymond A. Serway, John W. Jewett

Publisher:Raymond A. Serway, John W. Jewett

Chapter24: Electromagnetic Waves

Section: Chapter Questions

Problem 55P

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A 2.50-m-diameter university communications satellite dish receives TV signals that have a maximum electric field strength (for one channel) of 7.50 (V/m. (See Figure 24.28.) (a) What is the intensity of this wave? (b) What is the power received by the antenna? (c) If the orbiting satellite broadcasts uniformly over an area of 1.501013m2 (a large fraction of North America), how much power does it radiate? Figure 24.28 Satellite dishes receive TV signals sent from orbit. Although the signals are quite weak, the receiver can detect them by being tuned to resonate at their frequency.
Professor Edward Ney was the founder of infrared astronomy at the University of Minnesota. In his later years, he wore an artificial pacemaker. Always an experimentalist, Ney often held a strong laboratory magnet near his chest to see what effect it had on his pacemaker. Perhaps he was using the magnet to throw switches that control different modes of operation. An admiring student (without an artificial pacemaker) thought it would be fun to imitate this great man by holding a strong magnet to his own chest. The natural pacemaker of the heart (known as the sinoatrial node) carries a current of about 0.5 mA. Estimate the magnetic force exerted on a natural pacemaker by a strong magnet held to the chest. How do you think the student might have felt during the experiment? Explain your geometric assumptions. Hints: See Table 30.1 (page 941) to estimate the magnetic field, and assume the field is roughly uniform. Use Figure P30.58 to estimate the size of the sinoatrial node; your heart is about the size of your fist. FIGURE P30.58
A particle of cosmic dust has a density =2.0g/cm3 , (a) Assuming the dust particles are spherical and light absorbing, and are at the same distance as Earth from the Sun, determine the particle size for which radiation pressure from sunlight is equal to the Sun's force of gravity on the dust particle, (b) Explain how the forces compare if the particle radius is smaller, (c) Explain what this implies about the sizes of dust particle likely to be present in the inner solar system compared with outside the Oort cloud.
(a) What is the wavelength of a 1.00-eV photon? (b) Find its frequency in hertz. (c) Identify the type of EM radiation.
A possible means of space flight is to place a perfectly reflecting aluminized sheet into orbit around the Earth and then use the light from the Sun to push this solar sail. Suppose a sail of area A = 6.00 105 m2 and mass m =6.00 103 kg is placed in orbit facing the Sun. Ignore all gravitational effects and assume a solar intensity of 1 370 W/m2. (a) What force is exerted on the sail? (b) What is the sails acceleration? (c) Assuming the acceleration calculated in part (b) remains constant, find the time interval required for the sail to reach the moon, 3.84 108 m away, starting from rest at the Earth.
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 P34.75
If you wish to detect details of the size of atoms (about 0.2 nm) with electromagnetic radiation, it must have a wavelength of about this size. (a) What is its frequency? (b) What type of electromagnetic radiation might this be?
A LASIK vision correction system uses a laser that emits 10-nsns-long pulses of light, each with 2.5 mJmJ of energy. The laser is focused to a 0.85-mmmm-diameter circle. What is the average power of each laser pulse? What is the electric field strength of the laser light at the focus point?
A radio antenna broadcasts a 1.0 MHz radio wave with 25 kW of power. Assume that the radiation is emitted uniformly in all directions.a. What is the wave’s intensity 30 km from the antenna?b. What is the electric field amplitude at this distance?
Laser Safety A 0.95 mW laser emits a narrow beam of light that enters the eye. d=5.0 um a. How much energy is absorbed by the eye in 0.20 s? b. The eye focuses this beam to a tiny spot on the retina, perhaps 5.0 μm in diameter. What is the average intensity of light at this spot?
a. Write down an E(z,t) and a B(z,t) travelling wave of an EM wave in terms of k and w. What are these constants and the speed of the wave in terms of the wavelength A and the frequency f of the wave? b. What are the energy densities stored in an electric and a magnetic field? c. What is the total instantaneous energy stored per unit volume in a region of space where there is an EM wave? Seeing that that e = express this in terms of the B- field. d. Express the Poynting vector in terms of the B- field. e. What is the time averaged Poynting vector in terms of Eo or Bo (in terms of Ems or Bms). What is the intensity / of the wave?
the US, Verizon's new 5G signal uses electromagnetic waves of frequency 28 GHz, which is 28 x 10^9 Hz. a. What wavelength of light is this? b. What kind of electromagnetic wave is this (radio, infrared, x-ray, etc)? C. Your microwave oven uses electromagnetic waves of frequency 2.4 GHz or 2.4 x 10^9 Hz. The energy contained in a photon is directly proportional to its frequency. This means that: Everizon 28 x 10°HZ W hile EMicrowave Oven x 2.4 × 10°HZ How many times more energy does a photon from the Verizon cell signal have than the photon from your microwave? Compare that to the previous (4G LTE) signal of 700 MHz or 7 x 10^8 Hz. (Before you get too worried remember that total energy delivered is related to intensity as well, not just individual photon energy. You can blind yourself with a red laser, but not with a dim red penlight of the same frequency, for example). ace