Physics confusion !

[chanaykidaal]

What is the formula for magnetic flux linkage across a flat coil.. I learnt in class that it was BANcos x
However while solving the paper of Nov 2005, it was written in the marking scheme BAN sin x .. Can any body explain it to me !! Thank you

Q.6 part b Nov 2005

 

[msk]

BANsinx is the right formula because normally magnetic feild acts normal to the electric field so sin90 =1 we use BAN
but when it is acting at angle then it BANsinx!