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Chapter 38: Q13. (page 1114)

A 100 W incandescent lightbulb emits about 5 W of visible light. (The other 95 W are emitted as infrared radiation or lost as heat to the surroundings.) The average wavelength of the visible light is about 600 nm, so make the simplifying assumption that all the light has this wavelength. How many visible-light photons does the bulb emit per second?

Short Answer

Expert verified

1.5092×1019photons/sec

Step by step solution

01

Given Parameters.

Energy Emitted by bulb in form of visible light: 5W

Wavelength of Light: 600nm

02

Formula Used:

Energy of single photon = hcλ

Energy emitted by bulb in form of light per second : 5W = 5J/s

No. of photons emitted per second: EnergyemittedbybulbpersecondEnergyofphoton

5hcλ=5λhc=5J/s×600×10-9m6.626×10-34Js×3×108m/s=1.5092×1019photons/s

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Most popular questions from this chapter

The electron interference pattern of Figure 38.12 was made by shooting electrons with 50keVof kinetic energy through two slits spaced role="math" localid="1650737433408" 1.0μmapart. The fringes were recorded on a detector 1.0mbehind the slits.

a. What was the speed of the electrons? (The speed is large enough to justify using relativity, but for simplicity do this as a nonrelativistic calculation.)

b. Figure 38.12 is greatly magnified. What was the actual spacing on the detector between adjacent bright fringes?

What is the length of a one-dimensional box in which an electron in the n=1state has the same energy as a photon with a wavelength of 600nm?

A photoelectric-effect experiment finds a stopping potential of 1.56Vwhen light of 200nmis used to illuminate the cathode.

a. From what metal is the cathode made?

b. What is the stopping potential if the intensity of the light is doubled?

Very large, hot stars—much hotter than our sun—can be identified by the way in which He+ions in their atmosphere absorb light. What are the three longest wavelengths, in nm, in the Balmer series of He+?

FIGURE Q38.12 shows the energy-level diagram of Element X.

a. What is the ionization energy of Element X?

b. An atom in the ground state absorbs a photon, then emits a photon with a wavelength of 1240 nm. What was the energy of the photon that was absorbed?

c. An atom in the ground state has a collision with an electron, then emits a photon with a wavelength of 1240 nm. What conclusion can you draw about the initial kinetic energy of the electron?
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