Chap_30_Disc[1]

# Chap_30_Disc[1] - 30-27 You have two lightbulbs of...

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30-27: You have two lightbulbs of different power and color, as indicated in Figure 30– 21. One is a 150-W red bulb, and the other is a 25-W blue bulb. (a) Which bulb emits more photons per second? (b) Which bulb emits photons of higher energy? (c) Calculate the number of photons emitted per second by each bulb. Take red = 650 nm and blue = 460 nm (Most of the electromagnetic radiation given off by incandescent lightbulbs is in the infrared portion of the spectrum. For the purposes of this problem, however, assume that all of the radiated power is at the wavelengths indicated.) Picture the Problem : A 150-watt red light bulb emits photons with wavelength of 650 nm, and a 25-watt blue light bulb emits photons with a wavelength of 460 nm. Strategy: Combine equations 30-4 and 14-1 to find the energy of the photons for each bulb. Divide the emitted power by the energy of each photon to calculate the rate at which photons are emitted. Solution: 1. (a) The energy emitted per photon is inversely related to the wavelength, so the red light bulb must emit more photons to produce the same power output. The red bulb also produces more power than the blue bulb, so the red bulb emits more photons per second than does the blue bulb.

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Chap_30_Disc[1] - 30-27 You have two lightbulbs of...

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