Average Current in Coil Rotated in Magnetic Field

[dvolpe]

Homework Statement

A circular conducting coil of radius 2.8 cm is placed in a uniform magnetic field of .900 T with the plane of the coil perpendicular to magnetic field. Coil rotated 180 degrees about the axis in .222 seconds. If the coil is made of copper with a diameter of .900 mm, what is the average current that flows through the coil during the rotation?

Homework Equations

V = IR R = pL/A

The Attempt at a Solution

I correctly figured out the induced voltage of .02 V.
V = IpL/A
p of copper = 1.68e-7
L = 2pi*r A = pi*r squared so L/A = 2pi*r/pi*r sq. = 2/r
.02 V = I (1.68e-7)(2/.45e-3)
I = .00267e4

The answer per the webassign is 4.32 A. HELP!

 

[SammyS]

Homework Statement

A circular conducting coil of radius 2.8 cm is placed in a uniform magnetic field of .900 T with the plane of the coil perpendicular to magnetic field. Coil rotated 180 degrees about the axis in .222 seconds. If the coil is made of copper with a diameter of .900 mm, what is the average current that flows through the coil during the rotation?

Homework Equations

V = IR R = pL/A

The Attempt at a Solution

I correctly figured out the induced voltage of .02 V.
V = IpL/A
p of copper = 1.68e-7
L = 2pi*r  This is the radius of the coil: r_c = 2.8 cm .

       A = pi*r squared   This is half the diameter of the copper wire: r_w = 0.450 mm .

                   so L/A = 2pi*r_c/(pi*r_w²) = 2r_c/r_w²

.02 V = I (1.68e-7)(2/.45e-3)
I = .00267e4

The answer per the webassign is 4.32 A. HELP!

Those r's are not the same, so they don't cancel.