To solve this problem it is necessary to apply the definition given in Faraday's law in a solenoid for which it is noted that


Where,
N = Number of loops
A = Cross sectional Area
B = Magnetic Field



Therefore the correct answer is A.
I'm pretty sure it is true. (78% sure)
Water equal to iron is greater than cooper
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The answer is C. the earths mantle because the wood in this case is the surface