Calculate Initial Magnitude B of Uniform Magnetic Field

[golriz]

A conducting loop has an area of A=0.065 m^2 and is positioned such that a uniform magnetic field points at θ = 60 degrees relative to the plane of the loop. When the magnitude of the magnetic field decreases to B(f) = 0.30 T in ∆t = 0.087s , the average induced emf in the loop is average ε= 1.2V. Calculate the initial magnitude B(i) of the magnetic field.


ε = -∆Ф/∆t = -( ABcosθf - ABcosθi )/∆t
1.2 = - 0.065( B(f) - B(i) )/0.087 = - 0.065( 0.30 - B(i) )/ 0.087
B(i) = 1.9 T

I think since in the question is said a uniform magnetic field so "B" should be constant and θ should change.

 

[diazona]

No, uniform simply means that at any given moment, B and θ are the same at all points in space. They can both change with time (although in this problem I see nothing to indicate that θ changes).