帮我讲解一下这道题目---Here's a complete and accurate extraction of the content from the image, formatted as requested:
**Question Stem:**
2. 如图所示，xOy 平面的第一、三象限内以坐标原点 O 为圆心、半径为 $\sqrt{2}L$ 的扇形区域充满方向垂直纸面向外的匀强磁场。边长为 L 的正方形金属框绕其始终在 O 点的顶点、在 xOy 平面内以角速度 ω 顺时针匀速转动，t=0 时刻，金属框开始进入第一象限。不考虑自感影响，关于金属框中感应电动势 E 随时间 t 变化规律的描述正确的是（ ）
**(Translation for clarity, not part of the output requirements but useful for understanding):**
As shown in the figure, in the first and third quadrants of the xOy plane, a sector region with the origin O as the center and a radius of $\sqrt{2}L$ is filled with a uniform magnetic field pointing perpendicularly out of the paper. A square metal frame of side length L rotates uniformly clockwise with an angular velocity ω in the xOy plane, with one of its vertices always fixed at point O. At t=0, the metal frame begins to enter the first quadrant. Ignoring self-induction effects, which description of the change in the induced electromotive force E in the metal frame with time t is correct?
**Chart/Diagram Description:**
* **Type:** Cartesian coordinate system showing a rotating square metal frame within a magnetic field region.
* **Coordinate Axes:** X-axis labeled 'x' pointing right, Y-axis labeled 'y' pointing up. The origin is labeled 'O'.
* **Square Metal Frame:** A square of side length L. One vertex is fixed at the origin O.
* **Initial Position (solid lines):** At t=0, the square is entirely in the first quadrant (x≥0, y≥0). Its two sides adjacent to the origin O are aligned with the positive X-axis and positive Y-axis, respectively.
* **Rotated Position (dashed lines):** The square is shown rotated clockwise from its initial position.
* **Rotation:** A curved arrow near the top-left corner of the square indicates clockwise rotation around the origin O, with angular velocity 'ω'.
* **Magnetic Field Region:** The problem states the magnetic field is present in the first and third quadrants as a sector with center O and radius $\sqrt{2}L$. The side length of the square is L, so its diagonal is $L\sqrt{2}$. This means the outermost vertex of the square is always within or on the boundary of this circular region as it rotates.
* **Magnetic Field Direction:** Two points labeled 'B' (one in the first quadrant, one in the third quadrant) are shown as dots (•), indicating that the uniform magnetic field points perpendicularly out of the paper.
**Options:**
A. 在 t=0 到 t=$\frac{\pi}{2ω}$ 的过程中，E 一直增大
(In the process from t=0 to t=$\frac{\pi}{2ω}$, E continuously increases)
B. 在 t=0 到 t=$\frac{\pi}{2ω}$ 的过程中，E 先增大后减小
(In the process from t=0 to t=$\frac{\pi}{2ω}$, E first increases then decreases)
C. 在 t=0 到 t=$\frac{\pi}{4ω}$ 的过程中，E 的变化率一直增大
(In the process from t=0 to t=$\frac{\pi}{4ω}$, the rate of change of E continuously increases)
D. 在 t=0 到 t=$\frac{\pi}{4ω}$ 的过程中，E 的变化率一直减小
(In the process from t=0 to t=$\frac{\pi}{4ω}$, the rate of change of E continuously decreases)