Question

in science class, students built the device pictured below using cardboard, wires, pipes, compasses, and a battery. 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 electricity is flowing through the compass needles, causing them to turn toward the wire. b. the current creates a magnetic field that exerts a force on the compass needles. 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.

Explanation:

This is based on the principle of electromagnetism. When an electric - current flows through a wire, it generates a magnetic field around the wire. This magnetic field exerts a force on the magnetic compass needles, causing them to change direction. Option A is incorrect as electricity does not flow through the compass needles in this setup. Option C is wrong because compasses do not create their own electric fields that would cause such a rotation. Option D is incorrect since the Earth's magnetic field does not change direction due to this local electric - current connection.

Answer:

B. The current creates a magnetic field that exerts a force on the compass needles.