University Physics with Modern Physics (14th Edition)
14th Edition
ISBN: 9780321973610
Author: Hugh D. Young, Roger A. Freedman
Publisher: PEARSON
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Chapter 38, Problem 38.7DQ
To determine
The reason for human skin being insensitive to visible light but severe burns are caused by ultraviolet
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Human skin is relatively insensitive to visible light, but ultraviolet radiation can cause severe burns. Does this have anything to do with photon energies? Explain.
A certain helium-neon laser pointer, emitting light with a wavelength of 632 nm, has a beam with an intensity of 715 W/m2 and a diameter of 2.70 mm. How many photons are emitted by the laser pointer every second?
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Exposure to a sufficient quantity of ultraviolet light will redden the skin, producing erythema—a sunburn. The amount of exposure necessary to produce this reddening depends on the wavelength. For a 1.0 cm2 patch of skin, 3.7 mJ of ultraviolet light at a wavelength of 254 nm will produce reddening; at 300 nm wavelength, 13 mJ are required.a. What is the photon energy corresponding to each of these wavelengths?b. How many total photons does each of these exposures correspond to?c. Explain why there is a difference in the number of photons needed to provoke a response in the two cases.
Chapter 38 Solutions
University Physics with Modern Physics (14th Edition)
Ch. 38.1 - Silicon films become better electrical conductors...Ch. 38.2 - Prob. 38.2TYUCh. 38.3 - Prob. 38.3TYUCh. 38.4 - Prob. 38.4TYUCh. 38 - Prob. 38.1DQCh. 38 - Prob. 38.2DQCh. 38 - Prob. 38.3DQCh. 38 - Prob. 38.4DQCh. 38 - Prob. 38.5DQCh. 38 - Prob. 38.6DQ
Ch. 38 - Prob. 38.7DQCh. 38 - Prob. 38.8DQCh. 38 - Prob. 38.9DQCh. 38 - Prob. 38.10DQCh. 38 - Prob. 38.11DQCh. 38 - Prob. 38.12DQCh. 38 - Prob. 38.13DQCh. 38 - Prob. 38.14DQCh. 38 - Prob. 38.15DQCh. 38 - Prob. 38.16DQCh. 38 - Prob. 38.17DQCh. 38 - Prob. 38.1ECh. 38 - Prob. 38.2ECh. 38 - Prob. 38.3ECh. 38 - Prob. 38.4ECh. 38 - Prob. 38.5ECh. 38 - Prob. 38.6ECh. 38 - Prob. 38.7ECh. 38 - Prob. 38.8ECh. 38 - Prob. 38.9ECh. 38 - Prob. 38.10ECh. 38 - Prob. 38.11ECh. 38 - Prob. 38.12ECh. 38 - Prob. 38.13ECh. 38 - Prob. 38.14ECh. 38 - Prob. 38.15ECh. 38 - Prob. 38.16ECh. 38 - Prob. 38.17ECh. 38 - Prob. 38.18ECh. 38 - Prob. 38.19ECh. 38 - Prob. 38.20ECh. 38 - Prob. 38.21ECh. 38 - An electron and a positron are moving toward each...Ch. 38 - Prob. 38.23ECh. 38 - Prob. 38.24ECh. 38 - Prob. 38.25ECh. 38 - Prob. 38.26PCh. 38 - Prob. 38.27PCh. 38 - Prob. 38.28PCh. 38 - Prob. 38.29PCh. 38 - Prob. 38.30PCh. 38 - Prob. 38.31PCh. 38 - Prob. 38.32PCh. 38 - Prob. 38.33PCh. 38 - Prob. 38.34PCh. 38 - Prob. 38.35PCh. 38 - Prob. 38.36PCh. 38 - Prob. 38.37PCh. 38 - Prob. 38.38PCh. 38 - Prob. 38.39PCh. 38 - Prob. 38.40CPCh. 38 - Prob. 38.41PPCh. 38 - Prob. 38.42PPCh. 38 - Prob. 38.43PPCh. 38 - Prob. 38.44PPCh. 38 - Prob. 38.45PP
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- (a) If the power output of a 650-kHz radio station is 50.0 kW, how many photons per second are produced? (b) If the radio waves are broadcast uniformly in all directions, find the number of photons per second per square meter at a distance of 100 km. Assume no reflection from the ground or absorption by the air.arrow_forwardHow many x-ray photons per second are created by an x ray tube that produces a flux of x rays having a power of 1.00 W? Assume the average energy per photon is 75.0 keV.arrow_forward(a) What is the maximum energy in eV of photons produced in a CRT using a 25.0-kV accelerating potential, such as a color TV? (b) What is their frequency?arrow_forward
- (a) Calculate the number of photoelectrons per second ejected from a 1.00-mm2 area of sodium metal by 500-nm M radiation having an intensity of 1.30 kW/m2 (the intensity of sunlight above the Earth's atmosphere). (b) Given that the binding energy is 2.28 eV, what power is carried away by the electrons? (c) The electrons carry away less power than brought in by the photons. Where does the other power go? How can it be recovered?arrow_forwardIntegrated Concepts A certain heat lamp emits 200 W of mostly IR radiation averaging 1500 nm in wavelength. (a) What is the average photon energy in joules? (b) How many of these photons are required to increase the temperature of a person's shoulder by 2.0°C, assuming the affected mass is 4.0 kg with a specific heat of 0.83kcal/kgC. Also assume no other significant heat transfer. (c) How long does this take?arrow_forward(a) Find the momentum of a 4.00-cm-wavelength microwave photon. (b) Discuss why you expect the answer to (a) to be very small.arrow_forward
- (a) How far away must you be from a 650-kHz radio station with power 50.0 kW for there to be only one photon per second per square meter? Assume no reflections or absorption, as if you were in deep outer space. (b) Discuss the implications for detecting intelligent life in other solar systems by detecting their radio broadcasts.arrow_forward(a) Find the energy in joules and eV of photons in radio waves from an FM station that has a 90.0-MHz broadcast frequency. (b) What does this imply about the number of photons per second that the radio station must broadcast?arrow_forward(a) Calculate the velocity of an electron that has a wavelength of 1.00 m. (b) Through what voltage must the electron be accelerated to have this velocity?arrow_forward
- A 600-nm light falls on a photoelectric surface and electrons with the maximum kinetic energy of 0.17 eV are emitted. Determine (a) the work function and (b) the cutoff frequency of the surface. (c) What is the stopping potential when the surface is illuminated with light of wavelength 400 nm?arrow_forwardThe velocity of a proton emerging from a Van de Graaff accelerator is 25.0% of the speed of light. (a) What is the proton's wavelength? (b) What is its kinetic energy, assuming it is nonrelativistic? (c) What was the equivalent voltage through which it was accelerated?arrow_forwardIKIM FM radio station in Klang Valley is being brodcasted at 91.5 MHz with a radiation power of 50.0 kW. Determine: i) The momentum of each photon. ii) The energy of each photon. iii) The amount of photons emitted by IKIM FM in each second.arrow_forward
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