# Chapter 20 - Traveling Waves - Exercises and Problems: 65

(a) $P = 6.7\times 10^4~W$ (b) $I = 8.5\times 10^{10}~W/m^2$

#### Work Step by Step

(a) We can find the power of one laser pulse as: $P = \frac{E}{t}$ $P = \frac{1.0\times 10^{-3}~J}{15\times 10^{-9}~s}$ $P = 6.7\times 10^4~W$ (b) The light from the laser does not spread out as it leaves the laser. The light stays in a beam with a diameter of 1.0 mm. We can find the light intensity of the light wave as: $I = \frac{P}{A}$ $I = \frac{P}{\pi~R^2}$ $I = \frac{6.7\times 10^4~W}{(\pi)(0.5\times 10^{-3}~m)^2}$ $I = 8.5\times 10^{10}~W/m^2$

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