Do you know what is the rate of change of magnetic flux linkage in this question?
The rate of change of the magnetic field is the gradient of the B vs t graph.
Let's say the magnitude of the gradients from 0 to t
1 and from t
1 to t
2 are B1 and B2, respectively.
As I have mentioned in post #2, the slope from t
1 to t
2 is steeper than that of the slope from 0 to t
1, so B2 is greater than B1 in magnitude.
When we consider the sign of the gradients and Lenz’s law, the induced emf from 0 to t1 would be positive. Why?
Do the same analysis from t
1 to t
2. The induced emf would be –B2.
Remember, B2 > B1 (magnitude only), so the graph has to be C.