EBK COLLEGE PHYSICS
3rd Edition
ISBN: 9780321989246
Author: Knight
Publisher: PEARSON CO
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Chapter 28, Problem 61GP
To determine
The current required to produce 5 mW of light.
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A light-emitting diode (LED) connected to a 3.0 V power supply emits 440 nm blue light. The current in the LED is 10 mA, and the LED is 60% efficient at converting electric power input into light power output. How many photons per second does the LED emit?
The human eye can barely detect a star whose intensity at the earth’s surface is 1.6 x 10-11 W/m2. If the dark-adapted eye has a pupil diameter of 7.0 mm, how many photons per second enter the eye from the star? Assume the starlight has a wavelength of 550 nm.
A 193-nm-wavelength UV laser for eye surgery emits a 0.500 mJ pulse. How many photons does the light pulse contain?
Chapter 28 Solutions
EBK COLLEGE PHYSICS
Ch. 28 - Prob. 1CQCh. 28 - Prob. 2CQCh. 28 - Prob. 3CQCh. 28 - Prob. 4CQCh. 28 - Prob. 5CQCh. 28 - Prob. 6CQCh. 28 - Prob. 7CQCh. 28 - Prob. 8CQCh. 28 - Prob. 9CQCh. 28 - Prob. 10CQ
Ch. 28 - Prob. 11CQCh. 28 - Prob. 12CQCh. 28 - Prob. 13CQCh. 28 - Prob. 14CQCh. 28 - Prob. 15CQCh. 28 - Prob. 16CQCh. 28 - Prob. 17CQCh. 28 - Prob. 18CQCh. 28 - Prob. 19CQCh. 28 - Prob. 20CQCh. 28 - Prob. 21CQCh. 28 - Prob. 22CQCh. 28 - Prob. 23CQCh. 28 - Prob. 24CQCh. 28 - Prob. 25CQCh. 28 - Prob. 26MCQCh. 28 - Prob. 27MCQCh. 28 - Prob. 28MCQCh. 28 - Prob. 29MCQCh. 28 - Prob. 30MCQCh. 28 - Prob. 31MCQCh. 28 - Prob. 32MCQCh. 28 - Prob. 33MCQCh. 28 - Prob. 34MCQCh. 28 - Prob. 35MCQCh. 28 - Prob. 1PCh. 28 - Prob. 2PCh. 28 - Prob. 3PCh. 28 - Prob. 4PCh. 28 - Prob. 5PCh. 28 - Prob. 6PCh. 28 - Prob. 7PCh. 28 - Prob. 8PCh. 28 - Prob. 9PCh. 28 - Prob. 10PCh. 28 - Prob. 11PCh. 28 - Prob. 12PCh. 28 - Prob. 13PCh. 28 - Prob. 14PCh. 28 - Prob. 15PCh. 28 - Prob. 16PCh. 28 - Prob. 17PCh. 28 - Prob. 18PCh. 28 - Prob. 19PCh. 28 - Prob. 20PCh. 28 - Prob. 21PCh. 28 - Prob. 22PCh. 28 - Prob. 23PCh. 28 - Prob. 24PCh. 28 - Prob. 25PCh. 28 - Prob. 26PCh. 28 - Prob. 27PCh. 28 - Prob. 28PCh. 28 - Prob. 29PCh. 28 - Prob. 30PCh. 28 - Prob. 31PCh. 28 - Prob. 32PCh. 28 - Prob. 33PCh. 28 - Prob. 34PCh. 28 - Prob. 35PCh. 28 - Prob. 36PCh. 28 - Prob. 37PCh. 28 - Prob. 38PCh. 28 - Prob. 39PCh. 28 - Prob. 40PCh. 28 - Prob. 41PCh. 28 - Prob. 42PCh. 28 - Prob. 43PCh. 28 - Prob. 44PCh. 28 - Prob. 45PCh. 28 - Prob. 46PCh. 28 - Prob. 47PCh. 28 - Prob. 48PCh. 28 - Prob. 49PCh. 28 - Prob. 50GPCh. 28 - Prob. 51GPCh. 28 - Prob. 52GPCh. 28 - Prob. 53GPCh. 28 - Prob. 54GPCh. 28 - Prob. 55GPCh. 28 - Prob. 56GPCh. 28 - Prob. 57GPCh. 28 - Prob. 58GPCh. 28 - Prob. 59GPCh. 28 - Prob. 60GPCh. 28 - Prob. 61GPCh. 28 - Prob. 62GPCh. 28 - Prob. 63GPCh. 28 - Prob. 64GPCh. 28 - Prob. 65GPCh. 28 - Prob. 66GPCh. 28 - Prob. 67GPCh. 28 - Prob. 68GPCh. 28 - Prob. 69GPCh. 28 - Prob. 70GPCh. 28 - Prob. 71GPCh. 28 - Prob. 72GPCh. 28 - Prob. 73GPCh. 28 - Prob. 74GPCh. 28 - Prob. 75GPCh. 28 - Prob. 76GPCh. 28 - Prob. 77GPCh. 28 - Prob. 78GPCh. 28 - Prob. 79GPCh. 28 - Prob. 80GPCh. 28 - Prob. 81GPCh. 28 - Prob. 82GPCh. 28 - Prob. 83GPCh. 28 - Prob. 84GPCh. 28 - Prob. 85MSPPCh. 28 - Prob. 86MSPPCh. 28 - Prob. 87MSPPCh. 28 - Prob. 88MSPP
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- A dental X-ray typically affects 215 g of tissue and delivers about 3.95 µJ of energy using X-rays that have wavelengths of 0.0235 nm. What is the energy in electron volts of a single photon of these X-rays? energy of a photon: eV How many photons are absorbed during the dental X-ray? number of photons absorbed: photonsarrow_forwardA photon has 2.90 eV of energy. What is the photon’s wavelength? (h = 6.626 x 10-34, 1 eV = 1.6 x 10-19 J) 677 nm 428 nm 345 nm 218 nmarrow_forwardWhat is the energy (in eV) of a photon with 150 nm wavelength?arrow_forward
- Three laser beams have wavelengths λ1 = 400 nm, λ2 = 600 nm, and λ3 = 800 nm. The power of each laser beam is 1 W.a. Rank in order, from largest to smallest, the photon energies E1 , E2 , and E3 in these three laser beams. Explain.b. Rank in order, from largest to smallest, the number of photons per second N1 , N2 , and N3 delivered by the three laser beams. Explain.arrow_forwardHow many photons are emitted per second from a semiconductor laser which emits 0.75mW of light at a wavelength of 540 nm?arrow_forwardWhen the scientist shines light of frequency f on the cathode, the galvanometer G measures a current of i. How could the scientist gradually reduce the current to zero? Gradually alter the electric field to create a sufficiently large reverse potential across the electrodes. Gradually increase the frequency of the light. Gradually decrease the intensity of light to one half its initial value.arrow_forward
- A limitation on how many spectra per second can be recorded by a time-of-flight mass spectrometer is the time it takes the slowest ion to go from the source to the detector. Suppose we want to scan up to m/z 500 for ions with z = 1. Calculate the speed of this heaviest ion if it is accelerated through 5.00 kV in the source. How long would it take to drift 2.00 m through a spectrometer? At what frequency could you record spectra if a new extraction cycle were begun each time the heaviest ion reached the detector? What would be the frequency if you wanted to scan up to m/z 1000?arrow_forwardThe human eye is a complex sensing device for visible light. The optic nerve needs a minimum of 2.0 10-17 J of energy to trigger a series of impulses that eventually reach the brain. How many photons of blue light (470. nm) are needed?arrow_forwardA recent study found that electrons that have energies between 3.45 eV and 20.5 eV can cause breaks in a DNA molecule even though they do not ionize the molecule. If a single photon were to transfer its energy to a single electron, what range of light wavelengths could cause DNA breaks? minimum wavelength: radio In which part of the electromagnetic spectrum does this light lie? O ultraviolet infrared nm gamma ray maximum wavelength: nmarrow_forward
- A 633 nm helium-neon laser puts out 4.00 W of power with a beam 5.70 mm in diameter. The beam is pointed directly at a pinhole which has a diameter of 1.80 mm. How many photons of light will travel through the pinhole per second? Assume that the intensity of the light is equally distributed across the whole area of the beam. number of photons per second: photons/sarrow_forwardA cloud of 〖"2.5x10"〗^19 electrons move past a given point every 2seconds. How much is the intensity of the electron flow?arrow_forwardThe average threshold of dark-adapted (scotopic) vision is 4.00 x 10-11 W/m? at a central wavelength of 500 nm. If light having this intensity and wavelength enters the eye and the pupil is open to its maximum diameter of 8.50 mm, how many photons per second enter the eye?arrow_forward
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