Why don’t we use the magnetic field provided by the earth to generate electricity?
It sounds like a good idea, but it’s not very practical. Before we explain why, let’s understand how we generate electricity, in case anyone reading this doesn’t already know.
Electricity (we say “current”) is created when charged particles flow, like water in a pipe. There are two kinds of electric charges – positive and negative.
Positive charges attract negative charges, but two particles with the same charge (both positively charged or both negatively charged) repel each other. This means they will separate. In other words, opposites attract.
Normally, electric current is made of tiny negative charges from atoms called “electrons”.
Everything we can touch is made of atoms. Each atom is surrounded by a cloud of electrons, which, like bees moving randomly around a hive, are attracted to the positive charge at the atom’s center (or “nucleus”).
Electric current usually occurs when electrons leave atoms and flow to other atoms.
how to generate electricity
There are three main ways we generate electricity.
First is the battery. In a battery, there is an “electrochemical reaction” that transfers electrons from one type of atom, which has a stronger attraction for the electrons, to another.
Batteries are designed to force these electrons through wires and into our electronic devices.
The second method is solar cells. The light energy is absorbed by the electrons in a substance called a “semiconductor” (usually silicon), which moves the electrons, creating an electric current.
The third method, moving a wire rapidly through a magnetic field, is often used to generate electricity for electrical outlets in our homes.
Generator working principle
Spin the coil in a strong magnetic field
You need to do this because the electrons in the wire can only feel the magnetic force when they are in motion.
In order to provide enough current, we have to move a lot of wires in the magnetic field. We do this by rapidly spinning a coil (of many coils) in a strong magnetic field.
With each turn of the coil, the electrons are stimulated by a magnetic field, causing them to move, which creates an electric current.
Falling water can be used (this is called “hydroelectricity”), steam (produced from coal, oil, gas, nuclear or solar power), wind turbines to spin the coils, and so on.
In most generators, the electrons get a magnetic kick every half turn of the coil. For the next half-turn, they get a magnetic kick in the opposite direction. This means that the direction of the current keeps switching rapidly over many cycles.
The current that switches directions is called “alternating current”, or AC for short. The battery only generates current in one direction, which is “direct current”, or DC for short.
In a generator, we are not absorbing energy from a magnetic field. The energy going into the current actually comes from the energy used to spin the coil.
Back to Earth’s Magnetic Field
Now back to the question: why don’t we use the Earth’s magnetic field to generate electricity?
The magnitude of the current generated by the generator mainly depends on at least three aspects: 1. How many coil loops are in the coil, 2. How fast the coil rotates, and 3. How big is the magnetic field.
The earth’s magnetic field is very weak, even if we use it to generate electricity, the current we can get is very small.
How small? Have you ever seen those button-shaped NdFeB magnets?
Their magnetic fields are about 6,000 times stronger than Earth’s magnetic field. The magnetic field inside the generator is about as strong as this.
Even refrigerator magnets have a magnetic field 200 times stronger than Earth’s magnetic field.
Don’t think that the larger the size, the bigger the magnetic field!