Describe Oersted's observation.

(N/A) As shown in the figure,a conducting wire is connected to a battery.
$A$ magnetic needle is placed near the conducting wire,which is stable in the North-South direction.
When the key is closed,the current flowing through the straight wire causes a deflection in the nearby magnetic compass needle. The alignment of the needle becomes tangential to an imaginary circle that has the straight wire as its center and its plane perpendicular to the wire. This situation is depicted in figure $(a)$.
Here,the needle is sufficiently close to the wire so that the Earth's magnetic field may be ignored.
Reversing the direction of the current reverses the orientation of the needle,which is depicted in figure $(b)$.
The deflection increases upon increasing the current or bringing the needle closer to the wire. This observation leads to the conclusion that moving charges or currents produce a magnetic field in the surrounding space.