The problem states that initially the wire coil is oriented perpendicular to a m

Question

The problem states that initially the wire coil is oriented perpendicular to a magnetic field of 0.63T pointing up.  Over time the field is changed to one of 0.25T pointing down. We are solving for the average induced emf in the coil.  The solution provided uses Faraday's law = -A(B2-B1)/t.  My question lies in finding the changing in magnetic flux (B2-B1).  The solution shows (-±0.25T - 0.63T) giving the change in magnetic flux as a -0.88 T... why is the final magnetic field (B2) negative?  Shouldn't the problem be solved as (0.25T - 0.63T) giving the change in magnetic flux as -0.38 T?

Explanation / Answer

Magnetic field pointing upward is taken as positive and inpointing down is taken as negative.

Initial magnetic field B = 0.63 T

                                 B ‘ = -0.25 T

So, change in magnetic field = B ‘ – B

                                               = -0.25 T – 0.63 T

                                               = -0.88 T

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