# Finally.

Three question E&M I final today, roughly as follows. 1a. As a starting point, calculate the electric potential on the axis of a ring (radius a) of uniform charge. (trivial) 1b. Use the expansion in Legendre polynomials to do an off-axis extrapolation of 1a to find the potential everywhere. (Conceptually not bad, mathematically tedious) 1c.…

# T-Rex and Detective Work

Ryan North of the exceptionally brilliant and somewhat esoteric Dinosaur Comics penned a comic a while back about the possibility of being the perfect detective by using physics. Quoth T-Rex in the strip: Someone in the room says something to another person, and then they both leave. Assuming you know exactly how they moved when…

# Quick Quiz: Population Control and Sex Ratios

Sorry for the light blogging this week. Finals are this week and next, and so I’m pretty swamped. Today I’m going to pose a straightforward but slightly counterintuitive probability question, of the sort that in modified forms aren’t so uncommon in physics: A densely populated authoritarian state issues the following population control policy: each family…

# The Physics of Rapunzel

Our excellent physics blogger Chad Orzel has a post up about the thermodynamics of Goldilocks. Seems it’s a little questionable to have the porridge configured as it was in the old tale. A few wags in the comments complain that in a story with talking bears physics is the least of the concerns, but I…

# Sunday Function

“I’d like to open a savings account,” you tell your banker. “Excellent!, the banker says, “our savings accounts have an interest rate of 5% and an annual percentage yield of 5.127%. It’s a great deal and I think you’ll like it.” 5% interest is a great deal on a savings account these days. But what’s…

# Bose-Einstein Condensates, pt. 4

Well, we’ve explored some groundwork in three previous posts and so it’s time to put it all together. Why exactly do bosons have such weird behavior at very low temperatures, with a large fraction of their number crowding into a single quantum state? Let’s plow on. If you’re not familiar with the mathematics or the…