請問一題電子學

如圖一所示，運算放大器其開迴路增益為1000，開迴路輸出電阻為5kΩ，其他性質為理想。
1.若沒負載時，B 處的輸出電壓為多少？
2.若從輸出引出5mA 的電流，輸出電壓變為多少？等效的閉迴路輸出電阻為多少？

希望能有完整的計算過程，假如能附上解釋就更棒了。

avontube

(a) for no load, that is open circuit.  The voltage at point B is zero.
(b) for 5 mA to flow through,  1001*Vx / 5000 = 5 mA.  Vx is the voltage across the input terminal (+/-).  Solving the equation, Vx = 24.97 mV  The output is then equal to -24.97 mV.

Hope this is correct.  I learned the Op-Amp circuit 30 years ago.