I just did an exercise from the book "a student's guide to Maxwell's Equation". I like the book, because the author has detailed solutions on his website. However, I suspect that his solution is wrong on this one. Problem statement: "A conducting bar descends with speed v down conducting rails in the presence of a constant, uniform magnetic field pointing into the page, as shown in the figure. Write an expression for the emf induced in the loop" I've attached both my solution and the solution on the website. I thought that since the area is decreasing, the sign of the flux change should be negative. Since speed must be a positive scalar, I just put a minus sign there. Thanks for any help!