Why does the EMF become 2Δ∅/Δt in this problem?

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HelpMeh
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Hi


Could someone explain why

ε=Δ∅/Δt

becomes 2∅/Δt?? i don't see how the change in magnetic flux is 2∅.
 
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  • Textbook solution showing average induced current Iav = ε/R, emf ε = ΔΦ/Δt = 2Φm/Δt = 2NBA/Δt, then Iav = 2NBA/(RΔt) and numerical evaluation giving 800 μA.
    Screen Shot 2012-04-19 at 6.55.00 PM.png
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Discussion

the plane of the coil is flipped so that the normal to the plane becomes opposite. Therefore the flux is negative of what it was before, so the total change in flux is twice the absolute value of flux through the coil.
 

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