请解题!---**Question 15** **Question Stem:** 外转子半径 r₁, 内转子半径 r₂, 外转子以恒定角速度 ω₀ 转动。外转子处磁感应强度大小为 B, 长度为 L, 电阻为 R。 求: (Translation: Outer rotor radius r₁, inner rotor radius r₂. The outer rotor rotates with a constant angular velocity ω₀. The magnetic induction intensity at the outer rotor is B, length is L, resistance is R. Find:) **Sub-questions:** (1) 内转子固定, ab 边感应电动势大小 E; (Translation: (1) The inner rotor is fixed, the magnitude of the induced electromotive force in side ab is E;) (2) 内转子固定, abcd 转一圈产生的热量; (Translation: (2) The inner rotor is fixed, the heat generated when abcd rotates one full turn;) (3) 内转子解除固定, 在外转子带动下以恒定角速度转动, abcd 中电流大小为 I, 求 abcd 中电流变化周期。 (Translation: (3) The inner rotor is released from fixation, rotating with a constant angular velocity driven by the outer rotor. The current in abcd is I. Find the period of current change in abcd.) --- **Chart/Diagram Description:** **Diagram 1 (Left Image):** * **Type:** 3D perspective view of a coaxial cylindrical system with a longitudinal cut-away section. * **Main Elements:** * **Cylinders:** Two concentric cylinders are shown. The inner cylinder has a cross-shaped pattern on its visible end face. The outer cylinder is partially cut away along its length to reveal the interior. * **Rectangular Loop (abcd):** A rectangular conductive loop labeled with vertices 'a', 'b', 'c', 'd' is positioned within the annular space between the inner and outer cylinders. * Sides 'ab' and 'cd' are parallel to the cylinder axis. 'a' and 'b' are on the inner surface of the outer cylinder. 'd' and 'c' are on the outer surface of the inner cylinder. * Sides 'ad' and 'bc' are radial segments connecting the inner and outer cylinders. * **Magnetic Field Regions:** The annular space is divided into distinct regions of magnetic field: * **Top Region:** Marked with dots (•), indicating a uniform magnetic field directed out of the plane (towards the viewer). The side 'ab' of the loop is in this region. * **Bottom Region:** Marked with crosses (×), indicating a uniform magnetic field directed into the plane (away from the viewer). The side 'cd' of the loop is in this region. * **Boundary Lines:** Dashed lines indicate the boundaries of the magnetic field regions and the radial extent of the loop. **Diagram 2 (Right Image):** * **Type:** 2D cross-sectional view (end view) of concentric circles with radial arrows. * **Main Elements:** * **Concentric Circles:** Two concentric circles represent the cross-section of the inner and outer rotors/cylinders. * **Magnetic Field Lines:** Multiple arrows are shown originating from the annular region between the two circles and pointing radially outwards from the center. These arrows represent the direction of the magnetic field in that region, indicating a radial magnetic field. The arrows are distributed uniformly around the circumference.