- #1
moenste
- 711
- 12
Homework Statement
A copper disc of radius 10 cm is situated in a uniform field of magnetic flux density 1.0 * 10-2 T with its plane perpendicular to the field.
The disc is rotated about an axis through its centre parallel to the field at 3.0 * 103 rev min-1. Calculate the EMF between the rim and centre of the disc.
Answer: 16 mV.
2. The attempt at a solution
Attempt 1
E = B A N ω, where ω = 2 π / T, where T = 1 / f.
f = 103 rev min-1 / 60 = 16.7 rev s-1.
ω = 2 π / 16.7 = 104.9 rad s-1.
E = 10-2 * (0.1 * 0.1) * 104.9 = 0.01049 V.
Attempt 2
I also used another formula: E = f B π (r22 - r12) where r2 = radius of rim, r1 = radius of axle.
E = 16.7 * 10-2 * π * 0.12 = 5.2 * 10-3 V.
What am I missing?