In order to observe the deflection of the small magnetic needle, the wire AB is parallel to the static direction of the small magnetic needle.

Because the wires are directly connected to the two poles of the power supply, the current is very large at this time, so the power-on time should be minimized and the switching time should be short.

So the answer is: when the wire AB is stationary, it is parallel to the direction of the small magnetic needle; Turn off the switch for a short time.