Astudent places a magnetic compass near an insulated copper wire with electric current moving through it. he notices that the compass needle no longer points north.
which of the following best explains this observation?
a. the magnetic poles that determine north and south reverse periodically.
b. the insulation prevents the compass from detecting earth's magnetic field.
c. the compass detects the magnetic field produced by the electric current.
d. the copper wire exerts an electrostatic force on the compass needle.

C. The compass detects the magnetic field produced by the electric current.

Explanation:

In 1820, Hans Christian Ørsted discovered that a magnetized needle placed in a direction parallel to an electric conductor was deflected when an electric current circulated through the conductor, evidencing the existence of a magnetic field around any conductor crossed by an electric current.

one person pulls 90n one way and the other has 100n pulling the other way.

so the net force = 90 - 100 = -10n,

or the ans can be 10n if the picture shows -90n and 100n instead.