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Why don't we use the magnetic energy that the earth provides to generate electricity?

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Why don't we use the magnetic energy that the earth provides to generate electricity? – student of Ms Brown's grade 5, class Neerim South Primary School, Victoria.


This sounds like a good idea first but it is not so practical. Before I explain why, let me first explain how we generate electricity if someone reads this does not already know.

Electricity (let's say "electric current") is when electrically charged particles float like water in a pipe. There are two types of electric charge ̵

1; positive and negative. Positive charges attract negative charges, but two particles with the same charge (both positive or both negative) will deviate. That means they push together.

In other words, opposites attract.

Usually, electric current is of small negative charges called "electrons" coming from atoms.

Everything you can touch is of atoms. Each atom is surrounded by an electron cloud that randomly beats as bees around a beehive, attracted to the positive charges of the atom (or "nucleus") of the atom.

An electric current usually occurs when electrons leave their atoms and floats to other atoms.

Read more:
Curious Children: How and why do the magnets stick together?

How to create an electric current

There are three main ways to produce electric current.

The first is batteries. In batteries, there is an "electrochemical reaction" that causes electrons to move from one type of atom to another type of atom with a stronger attraction for electrons. A battery is designed to force these electrons to pass through a wire in your electronic devices.

Another way is solar cells. Light energy is absorbed by electrons in something called "semiconductor" (usually silicon) that causes electrons to move and creates electrical current.

But I think you are asking about the third way commonly used to generate electric currents for power outlets in your house.

Spinning a Wire Coil in a Strong Magnetic Field

This third path is to move an electrical wire quickly through a magnetic field. You need to do it because electrons in a wire cannot feel the magnetic force if they do not move.

To get enough power for everyone, you have to move much wire through a magnetic field. We do this by spinning a coil (containing many loops) quickly in a strong magnetic field.

During each turn of the coil, electrons get a kick from the magnetic field and move them along. This creates electric current. In this animation, S represents the "south pole" of the magnet and N represents the "north pole". The animation shows only a single loop of wire spinning in the magnetic field. In a real generator there would be hundreds or even thousands of loops.

Machines that do this are called generators. You can spin the coil using falling water (it is called "hydro power"), steam (made from coal, oil, gas or heat from the sun), wind turbines using the wind and so on.

In most generators, every time the coil makes a half turn, electrons get a magnetic kick. In the next half tournament, they get a magnetic kick in the opposite direction. This means that the current is directed rapidly through many cycles.

Electric current that changes direction is called "alternating current" or AC for short. Batteries produce power that only moves in one direction, called "DC" or DC for short.

In generators, we do not take energy out of the magnetic field. The energy that goes into electric current actually comes from the energy used to spin the coil. Researchers call this "kinetic energy".

Back to Earth's magnetic field

Now (finally!) To answer your question: why don't we use the Earth's magnetic field to generate electricity?

The amount of current a generator produces depends mainly on at least three things: 1) how many wire bands in the coil, 2) how fast the coil spins and 3) how strong the magnetic field is.

The Earth's magnetic field is very weak, so you would get very little power from your generator.

How weak? Have you ever seen these button-shaped neodymium iron-boron magnets, also called "neo-magnets"? (Be careful – they can really squeeze you).

These magnets are small but powerful.
Flickr / wide Jordan, CC BY

They have magnetic fields around 6,000 times stronger than the Earth's magnetic field. Magnetic fields within electric generators are similar to this.

Cooling magnets also have magnetic fields about 200 times stronger than the earth's.

Read more:
Curious Children: Why Do Leaves Fall From Trees?

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