The magnetic flux Φ linked with a stationary coil behaves as follows: it remains constant from t=0 to 2s, then decreases uniformly with time from t=2s to 4s, and again becomes constant thereafter.
a. (i) In which time intervals is the induced emf in the coil zero?
b. (ii) In which time interval is it non-zero?
c. (iii) State whether the emf in the non-zero interval is positive or negative.