Lesson 8: Electromagnetism


What is electromagnetism?

Electro magnetism is the interaction of electric currents or fields and magnetic fields. 

Don’t worry if you don’t quite understand that yet.  You will after this lesson.

Electricity comes in two charges, positive and negative. 

Like charges repel, opposite charges attract. Two positive or two negative charges will repel.  A positive and negative charge will attract.

Magnetism is similar to electricity.  Magnets have two poles a north pole and a south pole.  The same poles will repel each other, and opposite poles attract.

What we have said so far may be a little bit miss leading. There is a magnetic field that surrounds magnetic objects. It is the field doing the attracting or repelling.  The stronger the field, the stronger the attraction or repulsion.  There are many factors that can affect the field strength of a magnet, including the size of the magnet, heat, radiation, and electric current, to name a few.

The magnetic field lines of a simple magnet are shown in the picture above.  They point from the north pole to the south pole.  However, the magnetic field lines do not just end at the tip of the magnet.  The go right through it so that inside the magnet, the magnetic field points from the south pole to the north.

You can place iron filings around a magnet, and as you see in the picture above, they will take the shape of the magnetic field.  Get a magnet and try it.  It is pretty cool.

Look at the picture above. The Earth itself is a magnet and has a magnetic field. The Earth’s magnetic field is believed to be generated by electric currents in its core created by heat escaping from the core.  Notice the earth’s north pole is actually its magnetic south pole and vice versa.

The Earth’s magnetic field should not be confused with its gravitational field.  There is also a gravitational field of force that surrounds the earth. A gravitational field is the region of space surrounding a body in which another body experiences a force of gravitational attraction. The gravitational field pulls objects like the moon to the earth.  It is not the earth itself that does the pulling. 

There is a relationship between electricity and magnetism. When you hold a magnet, it is the electric charges moving in the atoms that make it magnetic. You can make electricity by moving a magnet.  If you shake a magnet, it changes its magnetic field, and that creates an electric field.

It is now time to introduce James Clark Maxwell.  He developed four equations that cover everything needed to know about magnetism and electricity.  We are not going to go into detail on the equations.

In 1860 Maxwell introduced the world to electromagnetism.  His basic thought was if changing magnetic fields creates electric fields, then we should be able to change electric fields and make magnetic fields.  He was correct, and that led to the discovery of electromagnetic waves.

Electromagnetic waves are waves of electricity changing to magnetism, then magnetism changing to electricity, then electricity changing to magnetism, then magnetism changing to electricity, and so on and so on…

This changing of magnetism and electricity moves on its own through space as a wave of electromagnetic energy.  It is self-propagating, meaning it doesn’t need a medium to move through, like a water wave needs water or a sound wave needs air. It’s out there on its own.

Maxwell not only predicted electromagnetic waves but also predicted how fast they move through space.  Maxwell used his equations that we mentioned earlier to show an electromagnetic wave’s speed is 299,792,458 meters per second (it can go around the earth 7.5 times in one second) which is 670,616,629 miles per hour.  That was the speed of light.  Obviously, light was an electromagnetic wave.

That bears repeating.  Maxwell determined that electromagnetic waves moved at the speed of light therefore light was an electromagnetic wave. That was huge.  Do whatever you have to do to never forget that light is an electromagnetic wave.  Light being an electromagnetic wave is the foundation of our universe today.  Paint “light = electromagnetic wave” on a wall in your house (not really, unless you really want to.)  Just never, never, never forget that.  Not only is that important in this class.  It is so very important in your life.

Maxwell’s equations also showed there are other forms of electromagnetic waves besides light.  There are radio waves, microwaves, infrared waves, ultraviolet rays, x-rays, and gamma rays.  The waves differ by their frequency which is how rapidly they vibrate.  We will talk A LOT more about waves in later lessons.

Remember in lesson four when we said your heart produces electromagnetic waves created by your emotions?  How much better now can you visualize that?  

It’s kind of strange when you think about it, isn’t it?  Your heart is sending out alternating magnetic and electric waves, and so is your brain. Soon you are going to learn how to create the electromagnetic waves necessary to create your world.

We are going to stop here.  This lesson is a little short but so important.  We want to make sure you grasp everything we have just said.  We want to make sure those dendrites are clustering.  The information in this lesson is life-changing.

Draw your picture and teach someone else.  Make sure you see your picture many times a day.

Get ready!  Next lesson, we start covering Einstein’s Theory of Relativity.