Faraday's law -- Confusion about which Area to use in calculations

[yymm]

Homework Statement

Since magnetic flux(phi) is given by BA, is the A referring to the area that is generating the flux or is it referring to the area that's experiencing the change in flux? For example, in the first question, area would clearly be referring to the area of the loop right, but in the second example, the solutions substituted A=(0.02^2)pi, which is the area of the solenoid that is generating the flux? Doesn't it make more sense to use A as the area for the area of the loop thats experiencing the flux, which is (0.06^2)pi?

Relevant Equations

Ndphi/dt=emf

 

[nasu]

The flux is not BA in general. Only when the magnetic field is uniform and perpendicular to the surface the formula for flux has this simple form. Uniform means the same value and direction for all points of the area considered.
Do you think that this condition is satisfied for the flux throug the ring? Is the magnetic field (produced by the solenoid) uniform across the area of the ring?

 

[kuruman]

Doesn't it make more sense to use A as the area for the area of the loop thats experiencing the flux, which is (0.06^2)pi?

Only the area of the loop that is equal to the cross sectional area of the solenoid has magnetic flux through it. Outside the solenoid the magnetic field is zero therefore the flux through the rest of the loop's area is zero. That makes sense, no?

 

[yymm]

Only the area of the loop that is equal to the cross sectional area of the solenoid has magnetic flux through it. Outside the solenoid the magnetic field is zero therefore the flux through the rest of the loop's area is zero. That makes sense, no?
That makes complete sense! I forgot about it. Thanks!