Lesson 5: Electricity & Magnetism — Two Sides of One Force
Electricity & Magnetism — Two Sides of One Force
Electricity and magnetism seem completely different. One lights up your room. The other sticks notes to your fridge. But in the 1800s, physicists discovered they're actually two faces of the same fundamental force: electromagnetism.
Electric Charge
Everything is made of atoms. Atoms have a nucleus (protons with positive charge, neutrons with no charge) surrounded by electrons (negative charge). Normally atoms are balanced — equal protons and electrons.
When you rub a balloon on your hair, electrons transfer from your hair to the balloon. The balloon becomes negatively charged. Your hair becomes positively charged. Opposite charges attract — that's why the balloon sticks to the wall.
Like charges repel. Opposite charges attract. This is Coulomb's Law, and it follows the same inverse square pattern as gravity.
Electric Current
When charges flow continuously, that's electric current. In a wire, electrons drift from negative to positive. Current is measured in amperes (amps).
Voltage is the "pressure" pushing electrons through the wire — like water pressure in a pipe.
Resistance is how much the material fights against the flow.
Ohm's Law: V = IR (Voltage = Current × Resistance). This simple equation governs every circuit ever built.
Magnetism
Every magnet has a north and south pole. Like poles repel, opposite poles attract. Cut a magnet in half and you get two smaller magnets — each with their own north and south. You can never isolate a single pole.
Earth is a giant magnet. The molten iron in its core generates a magnetic field that extends into space and deflects harmful solar radiation. Without it, the solar wind would strip away our atmosphere over millions of years — exactly what happened to Mars.
The Connection: Moving Charges Create Magnetic Fields
This is the big discovery: an electric current creates a magnetic field around it. And a changing magnetic field creates an electric current. These two facts are the entire basis of:
- Electric motors (magnetism from electricity → rotation)
- Generators (rotation → electricity from magnetism)
- Transformers (changing magnetic fields → different voltages)
- Wireless charging (changing magnetic field in charger → current in your phone)
- Radio and Wi-Fi (oscillating electric and magnetic fields → electromagnetic waves)
Light Is an Electromagnetic Wave
James Clerk Maxwell figured out in 1865 that light is just oscillating electric and magnetic fields. Visible light, radio waves, microwaves, X-rays, gamma rays — all the same thing, just different frequencies. The entire electromagnetic spectrum is one unified phenomenon.
Think About It
- Why does your compass point north? What does that tell you about Earth's core?
- MRI machines use incredibly strong magnetic fields to image your body. How might that work?
- Why does your microwave heat food but visible light doesn't?