Starting position of coil in a generator I came across a few a.c. generator diagrams and I noticed for all of them the starting position of coil is vertical(area vector parallel to B vector)
Is there a reason for this? And if you can start in a horizontal position, would the emf graph look the same? (By start I mean when t=0)
 A: With the starting position of the coil that you quote, the flux linkage with the coil is $$N\Phi=BAN\cos \omega t.$$ Therefore the emf is $$\mathscr E =-\frac{d(N\Phi)}{dt} = BAN\omega \sin\omega t.$$ Here are two reasons for choosing this starting position. (a) It's usual to express the flux through an area in terms of the cosine of the angle between the magnetic field and the normal to the area. (b) It's convenient not to have a minus sign in the equation for emf (as you would if the coil had its normal at right angles to the field at time $t=0$).
[There is something of the tongue-in-cheek about (b)... (i) Since the emf is alternating, the presence or absence of a minus sign is usually of no interest at all. (ii) What does it even mean to say that the emf is positive or negative? If a load resistance were connected across the coil, which way round through the coil would the current have to be for the emf to be counted as positive? This question does have an answer, but perhaps it needs some thought.]
