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Question
Consider a closed loop C in a magnetic field (Figure). The flux passing through the loop is defined by choosing a surface whose edge coincides with the loop and using the formula φ = B1.dA1 + B2.dA2 +... Now if we chose two different surfaces S1 and S2 having C as their edge, would we get the same answer for flux. Jusity your answer.
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Solution
One gets the same answer for flux. Flux can be thought of as the number of magnetic field lines passing through the surface (we draw dN = B ∆ A lines in an area ∆ A ⊥to B), As lines of B cannot end or start in space (they form closed loops) number of lines passing through surface S1 must be the same as the number of lines passing through the surface S2.
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