Introduction To Health Physics
5th Edition
ISBN: 9780071835275
Author: Johnson, Thomas E. (thomas Edward), Cember, Herman.
Publisher: Mcgraw-hill Education,
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Chapter 14, Problem 14.25P
To determine
The power density, where the meter reading is +2.5 dB.
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Radio waves and microwaves are used in therapy to provide “deep heating” of tissue because the waves penetrate beneath the surface of the body and deposit energy. We define the penetration depth as the depth at which the wave intensity has decreased to 37% of its value at the surface. The penetration depth is 15 cm for 27 MHz radio waves. For radio frequencies such as this, the penetration depth is proportional to √λ, the square root of the wavelength.
If the frequency of the radio waves is increased, the depth of penetrationA. Increases. B. Does not change. C. Decreases.
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Chapter 14 Solutions
Introduction To Health Physics
Ch. 14 - Prob. 14.11PCh. 14 - Calculate the gain of a 30-cm-diameter parabolic...Ch. 14 - Prob. 14.13PCh. 14 - Prob. 14.14PCh. 14 - What is the maximum magnetic intensity in a plane...Ch. 14 - Prob. 14.16PCh. 14 - A rectangular horn antenna, 17cm24cm and operating...Ch. 14 - Prob. 14.18PCh. 14 - Prob. 14.19PCh. 14 - Prob. 14.20P
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- The Intensity of solar radiation at the Earth's orbit is 1370 W/m2. However, because of the atmosphere, the curvature of the Earth, and rotation (night and day), the actual intensity at the Earth's surface is much lower. At this moment, let us assume the intensity of solar radiation is 575 W/m2. You have installed solar panels on your roof to convert the sunlight to electricity. If the area of your solar panels is 4 m2, How much power is incident on your array? Watts Submit Answer Tries 0/2 Unfortunately, solar panels are only about 20% efficent...Only 1/5 of the light is converted to electricity. This being the case, how much electrical power are you actually producing for your home at this moment? Wattsarrow_forwardA source of electromagnetic waves radiates power uniformly in all directions at a single frequency. At a distance of 5.50 km from the source, a detector measures the intensity of the wave to be 26.0 μμW/m2. What is the average power radiated by the source?arrow_forwardRadio waves and microwaves are used in therapy to provide “deep heating” of tissue because the waves penetrate beneath the surface of the body and deposit energy. We define the penetration depth as the depth at which the wave intensity has decreased to 37% of its value at the surface. The penetration depth is 15 cm for 27 MHz radio waves. For radio frequencies such as this, the penetration depth is proportional to √λ, the square root of the wavelength. What is the wavelength of 27 MHz radio waves?A. 11 m B. 9.0 m C. 0.011 m D. 0.009 marrow_forward
- A certain radar installation that is used to track airplanes transmits electromagnetic radiation with a wavelength of 3.0 cmcm. Find the frequency of this radiation. Express your answer to two significant figures and include the appropriate units.arrow_forwardA microwave oven operates at 2.4 GHz with an intensity inside the oven of 2600 W/m2.arrow_forwardThe Earth has a radius of 6.38 x 106 m and is 1.50 x 1011 m from the Sun. The intensity of sunlight at the Earth is 1370 W/m2. a) At what rate does the Sun radiate energy? (This is the total power radiated by the Sun.) b) A solar sail is a large perfect reflector that gets pushed by the Sun's radiation. If there is a 2.5 km x 25. km solar sail that is perpendicular to the sun's radiation at the Earth's distance from the Sun, then what is the total radiation force of sunlight on the sail? c) What is the intensity of sunlight at Jupiter at a distance of 7.78 x 1011 m from the Sun?arrow_forward
- The average Earth–Sun distance is 1.00 astronomical unit (AU). At how many AUs from the Sun is the intensity of sunlight 1/49 the intensity at the Earth?arrow_forwardconsider a bright star in our sky. assume its distance from earth is 38.3 light-year (ly) and its power output is 4.00 * 10^28 W. about 100 times that of the sun. one light-year is the distance traveled by light through a vacuum in one year. a. find the intensity of the starlight at the earth. b. find the power of the starlight at the earth intercepts ( the radius of earth is 6.38 * 10^6 m .)arrow_forwardOperation of the pulse oximeter (see previous problem). The transmission of light energy as it passes through a solution of light-absorbing molecules is described by the Beer−Lambert law which gives the decrease in intensity I in terms of the distance L the light has traveled through a fluid with a concentration C of the light-absorbing molecule. The quantity ε is called the extinction coefficient, and its value depends on the frequency of the light. (It has units of m2/mol.) Assume the extinction coefficient for 660-nm light passing through a solution of oxygenated hemoglobin is identical to the coefficient for 940-nm light passing through deoxygenated hemoglobin. Also assume 940-nm light has zero absorption (ε = 0) in oxygenated hemoglobin and 660-nm light has zero absorption in deoxygenated hemoglobin. If 33% of the energy of the red source and 76% of the infrared energy is transmitted through the blood, what is the fraction of hemoglobin that is oxygenated?arrow_forward
- The frequency range for AM radio is 540 to 1600 kHz. The frequency range for FM radio is 88.0 to 108 MHz. Part (a) Caculate the maximum AND minimum wavelength for AM radio in meters. Part (b) Caculate the maximum AND minimum wavelength for FM radio in meters.arrow_forwardAssume the radiation from a heat lamp is monochromatic, with a wavelength of 1.5 μm . If the lamp’s 182.75-W output is focused on a person’s shoulder, over a circular area 26.5 cm in diameter, what is the intensity in kilowatts per square meter?arrow_forwardSuppose the maximum safe average intensity of microwaves for human exposure is 1.00 W/m2. Early radar units leaked radiation more than modern ones do, which caused identifiable health problems, such as cataracts, for people who worked near them. Part (a) If a radar unit leaks 6.5 W of microwave radiation uniformly in all directions, what is the closest distance, in centimeters, you can be to the unit and still be considered safe? Assume that the power spreads uniformly over the area of a sphere with no complications from absorption or reflection. Part (b) What is the maximum electric field strength E0, in volts per meter, of the microwave radiation at the maximum safe intensity?arrow_forward
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