Does magnetic flux change if the area is extended past the B field?

[gsquare567]

Homework Statement

A solenoid 2.50 cm in diameter and 30.0 cm long has 300 turns and carries 12.0 A. Calculate the flux through the surface of a disk of radius 5.00 cm that is positioned perpendicular to and centered on the axis of the solenoid.

Homework Equations

B = (permeability constant) * n * I
n is the number of turns per unit length, and I is the current

The Attempt at a Solution

n = 300 turns / 0.3 m = 1000
B is now known, but wouldn't the flux be the same for a disk of radius 2.50 cm and radius 5.00 cm, calculated as B * A = B * 2*pi*r^2, because the solenoid only has a radius of 2.5 cm and any greater than that doesn't matter?

Thanks =)

 

[ehild]

you are right if the disk is close enough.

http://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/imgmag/sol3.gif

ehild