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AP Physics C: E&M
13.3 Induced Currents and Magnetic Forces
13.2 Electromagnetic Induction
AdvancedMCQMathematicalProportional Analysis14.8k
A circular disk is viewed from above in a flat perspective. A central dot marks the rotation axis, with a curved counterclockwise arrow near the center labeled \(\omega_0\). A dashed radial reference line extends horizontally to the right from the center to the disk's outer edge, labeled \(R\). A small shaded circular patch represents the localized magnetic field region, centered on the horizontal line at a distance \(r_0\) from the central axis. Inside the small circular patch, exactly four small cross symbols indicate a magnetic field directed into the page, labeled \(B\). A straight dashed arrow tangent to the path of the patch points upward, indicating the local velocity. No other labels, lines, text, or axes appear.
Top view of a rotating conducting disk passing through a localized perpendicular magnetic field.
A thin, solid conducting disk of radius \(R\) and uniform thickness \(t_0\) rotates at a constant angular speed \(\omega_0\) about a perpendicular axis through its center. A uniform magnetic field of magnitude \(B\) is applied perpendicular to the plane of the disk over a small localized region centered at a distance \(r_0\) from the axis of rotation, generating eddy currents that exert a magnetic braking torque of magnitude \(\tau_0\) on the disk. The disk is replaced by a second disk made of the same conducting material and radius \(R\) but with thickness \(2t_0\), and it is rotated at an angular speed \(2\omega_0\) in the same magnetic field. What is the magnitude of the magnetic braking torque exerted on the second disk?

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