Corrections to Physics Demystified, 2nd edition On page 8, in the fourth line below the subheader "Rules for Use," you'll see the numeral 20,458,000,000. It should read as 24,580,000,000. On page 112, when I define mean life, I continue on to use quantified discussions in terms of a different specification, known as the half life. The mean life of a neutron is the average length of time that neutrons in isolation survive: about 15 minutes. The true half life is the length of time it takes for a large number of neutrons (say a million of them) to decrease to half the original number (say 500,000 of them). The half life is about 10 minutes. If we start with a large number of neutrons and allow the mean life to pass (about 15 minutes), we'll end up with 1/e, not 1/2, as many particles still intact. The symbol e represents the exponential constant, an irrational number that's quite close to 2.718281828459. Rounded down to six significant digits, 1/e = 0.367879. If we start with 1,000,000 particles and wait for the mean life to pass, we'll end up with 1,000,000 x 0.367879 = 367,879 particles, give or take a few from scenario to scenario. On page 535, Final Exam Question No. 90 should start out by saying, "Meteor-scatter propagation can occur ..." As it reads now, starting out with "Auroral communication," choices A, B, or C could all in theory be correct! The correct choice with this change would be A, as the answer key specifies. Last updated on May 21, 2016.