1. The problem statement, all variables and given/known data If the magnetic flux linking all of the turns of a 50 turn coil changes from 10 mWb to 20 mWb and induces an e.m.f. of 62.5 V in the coil, calculate the time over which the flux changes 2. Relevant equations Equation 1: E = - N x the change in flux / the change in time Equation 2: E = N x the change in flux / the change in time 3. The attempt at a solution I have seen this question on a number of occasions and the answer appear to be 0.8ms but my question is which is the correct equation to use? Equation 1 or Equation 2 and why are there 2 equations, one using -N and the other using N?