|
Electricity and magnetism |
In the 19th century, physics discovered these forces of nature.
| 1. | Electric charges are positive or negative. Like charges (both positive or both negative) repel, and opposite charges attract. |
| 2. | A similar situation is with magnetism. This is why a magnetic compass points to the north. Moving charges (currents) produce magnetism. Put a wire (and a resistor) between the poles of a battery so that a current will flow. Bring a compass nearby, and the needle will be affected by the current. |
| 3. | A changing magnetic field produces an electric field: Move a magnet closer to a closed wire, and current will flow. |
| 4. | A changing electric field produces a magnetic field: Charge up a plate capacitor, and there will be a magnetic field near the capacitor while the current is changing. |
It sounds so complicated. Maxwell wrote equations to describe this at the end of the 19th century. These are one of the most beautiful equations of physics. I feel it is worth the effort to learn the mathematics involved just to be able to understand these equations.
What comes out of these equations is light! A rapidly changing electric field produces a magnetic field. This rapidly changing magnetic field produces an electric field. These changes keep propagating. This is what light is!
While I was in college, I started thinking. Why did God create such a complicated universe, with all these complicated laws of nature: Charges attracting or repelling, electric currents creating magnetic fields, changing magnetic fields creating currents, etc.? Well, Einstein came in with his Theory of Special Relativity which shows that all these complicated things come just from charges attracting or repelling.
Sadly, high school students are not told this. They do not understand how Einstein unified the forces of charges, magnetism, and light into a single idea – forces between charges. One of the beautiful things about nature is its simplicity, when we get to understand this simplicity.
When we write the equations of electricity and magnetism, various constants appear.
SEE THE BOOK FOR MORE DETAILS.