?Note: Answers to all odd-numbered Problems, numbered in blue, can

Chapter 2, Problem 75

(choose chapter or problem)

Note: Answers to all odd-numbered Problems, numbered in blue, can be found in Appendix III. Exercises in the Problems by Topic section are paired, with each odd-numbered problem followed by a similar even-numbered problem. Exercises in the Cumulative Problems section are also paired but more loosely. Because of their nature, Challenge Problems and Conceptual Problems are unpaired.

An argon ion laser puts out 5.0 W of continuous power at a wavelength of 532 nm. The diameter of the laser beam is 5.5 mm. If the laser is pointed toward a pinhole with a diameter of 1.2 mm, how many photons will travel through the pinhole per second? Assume that the light intensity is equally distributed throughout the entire cross-sectional area of the beam. (1 W=1 J/s) Hint: Use the formula for the area of a circle \(\left(A=\pi r^{2}\right)\)  to find the cross-sectional area of the beam and of the pinhole and determine what fraction of the power gets through the pinhole.

Text Transcription:

A=pi r^2