Module 1, Challenge problem 1: I really didnt undrestand why we used A2 in equation phi=v.A while the limiting cross-sectional area is A1.
I mean the flux must pass the A1 first, we know its independent from A2. no matter how much do we increase A2, there will be no change in A1 and hence flux must be constant.

Question

Module 1, Challenge problem 1: I really didnt undrestand why we used A2 in equation phi=v.A while the limiting cross-sectional area is A1.
I mean the flux must pass the A1 first, we know its independent from A2. no matter how much do we increase A2, there will be no change in A1 and hence flux must be constant.

anonymous · Answer

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I think this sketch will show my mind better. the area of the path which the flux is going through it,  just depends on A1 and so we have $$\Phi=vA _{1}$$