The component of the external magnetic field along the central axis of a turn circular coil of radius cm decreases from t to t in s. if the resistance of the coil is ω, what is the magnitude of the induced current in the coil?

  I =  Δ(N*B*A) / R*Δt

                   and

               I= ΔФ / R*Δt

Explanation:

what is electromagnetic induction?

electromagnetic induction is a mechanism where current is induced in a coil or loop. To be specific Faraday's law of electromagnetic induction says that induced EMF is proportional to the induced current or emf.

FORMULA

I= ΔФ / R*Δt

BY EXPANDING THE FORMULA WE GET

ΔФ= Δ(N*B*A)  

by putting the value in equation we get:

I =  Δ(N*B*A) / R*Δt

where A is area of circular coil π*r²

DATA

N is number of turns in the coil

r  is radius of the circular coil

ΔB is  magnetic field

Δt is time

R is resistance of coil

the answer is the first electromagnet (a). this is because it has more coils around the ferromagnetic material. increasing the number of coils increases the surface area in which the metal interacts with the current in the coil. this enables more atoms in the metal to become aligned hence becoming more magnetized.