Question

Can electromagnetic force be decreased?

Answer 1

If you increase the current through th coils the magnetic strength will be increased.

Explanation:

Increase current to increase magnetic strength.
slide share net..So decreasing current will reduce magnetic strength.

Answer 2

This question is in the astronomy section, so we will look at it here from the viewpoint of the change in force of earth's magnetic field, and the answer is as definite YES!

Explanation:

The magnetic poles of the earth and its magnetism are the result of the liquid outer core around the slightly faster spinning solid inner core of the earth.

The difference in the spin rates added to the turbulence of the currents and viscose flow of the liquid outer core result in a magnetic field generated by the dynamo effect.

The magnetic force effect of the earth is not only increasing and decreasing, it is constantly moving, and has even inverted, or flipped over to become north-attracting at the geographic south pole.

There are plenty of images of the earth's magnetic poles, and they will all show the `S` pole deep inside the earth, at the core, pointing upward towards the geographic `N` pole. As we have learned, the north-attracting pole would need to be an `S` pole to cause a compass needle to point to it.

Before we get to the images, you really should read the information here from NASA. It encompasses a beautiful description:
https://science.nasa.gov/science-news/science-at-nasa/2003/29dec_magneticfield

The images are here:
https://commons.wikimedia.org/wiki/Category:Earth%27s_magnetic_field