Question

When there is no electricity running through the wire, all the compass needles point toward Earth’s magnetic north pole. When electric current is flowing through the wire, the compass needles change direction and point around the wire in a circle.

Why do the compass needles change direction when the electric current is flowing?
A.
The current creates a magnetic field that exerts a force on the compass needles.
B.
The electricity is flowing through the compass needles, causing them to turn toward the wire.
C.
The compasses create their own electric field, which forces their needles to rotate.
D.
The Earth’s magnetic field changes direction while the electricity is connected.

Answer 1

A.

Electric current in a wire produces a magnetic field that circles the wire (Oersted's discovery). The compass needle aligns with the net magnetic field (vector sum of the Earth's field and the wire's field), so when the wire's field is strong enough the needles turn to point around the wire (use the right‑hand rule to see the circular direction).