I have a conceptual question regarding the self-induced emf in a solenoid coil. I have attached a graphic from Serway's Physics for Scientists and Engineers (6th edition) from Chapter 32 (Inductance). My question is regarding induced emf's (called "Lenz's law emf" in figures (b) and (c)) in the coils; why are they in the shown configuration? It is my understanding that, according to Lenz's Law, the induced emf opposes a change in the magnetic flux of the region surrounded by the coil. By this logic, shouldn't the polarity in (b) be + | - (not - | + as shown) when the current is increasing, thus opposing the change in magnetic flux inside the solenoid and the opposite for (c) where the current is decreasing? Is there a typo, or am I missing something here? Thanks in advanced to anyone who can clarify the polarity of the induced emf for me!