A-2.37 µc point charge and a 4.74 µc point charge are a distance l apart.
where should a third point charge be placed so that the electric force on that third charge is zero? (hint: solve this problem by first placing the -2.37 µc point charge at the origin and place the 4.74 µc point charge at x = −l.)

I'm thinking it's 2 you are asked to explain the earth's magnetic field. which is the best reply? 1. the earth's magnetic south is similar to the north pole of a magnet. 2. the earth's core has a strong magnetic charge similar to the south pole of a magnet. 3. the earth's geomagnetic south is similar to the south pole of a magnet. 4. the earth's magnetic charge is not centered at either pole; it varies based on location.