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Why do not we use the Earth's magnetic energy to generate electricity?



Curious Kids is a series for children. If you have a question that an expert should answer, send it to curiouskids@theconversation.edu.au. You may also like the Podcast Imagine This, a co-production of ABC KIDS listen and The Conversation, based on Curious Kids.


Why do not we use the magnetic energy of the earth to generate electricity? – 5th grade students of Ms. Brown, Neerim South Primary School, Victoria.


Hi!

That sounds like a good idea, but not very practical. Before I explain why, let me first explain how we generate electricity if someone reading this does not yet know it.

Electricity (say "electric current") is when electrically charged particles, such as water, flow in a pipe. There are two types of electrical charge ̵

1; positive and negative. Positive charges attract negative charges, but two particles with the same charge (both positive or both negative) are repelled. That means they are pushing apart.

In other words, opposites attract.

Usually, electric current consists of tiny negative charges, called "electrons", which come from atoms.

Everything you can touch consists of atoms. Each atom is surrounded by an electron cloud that randomly moves like bees around a hive and is attracted by the positive charges in the center (or "core") of the atom.

An electric current normally arises when electrons leave their atoms and flow to other atoms.




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


How to generate electricity

We generate electricity in three ways.

The first are batteries. In batteries, there is an "electrochemical reaction" in which electrons move from one type of atom to another type of atom with a greater attraction to electrons. A battery should force these electrons to get through a wire into your electronic devices.

A second way is solar cells. Light energy is absorbed by electrons in so-called "semiconductors" (usually silicon), causing electrons to move and generate electrical current.

But I think you are asking for the third way that is normally used for generating electrical currents for power outlets in your home.

Spinning a Wire Spool in a Strong Magnetic Field

In this third method, an electric wire is rapidly moved through a magnetic field. You must do this because electrons in a wire can only sense the magnetic force as they move.

To get enough power for all, one has to move a lot of wire through a magnetic field. We quickly turn a coil (containing many wire loops) in a strong magnetic field.

With each revolution of the coil, electrons are pushed and moved by the magnetic field. This generates electricity. In this animation, S represents the south pole of the magnet and N the north pole. The animation shows only a single wire loop turning 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 turn the coil with falling water (that is, "water power"), steam (made from coal, oil, gas or heat from the sun), wind turbines that use the wind, etc.

In most generators Every time the coil makes a half turn, electrons get a magnetic kick. In the next half turn they get a magnetic kick in the opposite direction. This means that the direction of the current goes through many cycles quickly.

Electric current that changes direction is called "AC" or "AC" for short. Batteries generate electricity that flows in one direction, called "direct current" for short.

Generators do not extract energy from the magnetic field. The energy that flows into electrical current actually comes from the energy used to turn the coil. Scientists call this "kinetic energy".

Back to Earth's Magnetic Field

Now answer (finally!) Your question: why do not we use Earth's magnetic field to generate electricity?

The Amount of Current Generating a generator usually depends on at least three things: 1) how many wire loops in the coil, 2) how fast the coil is turned, and 3) how strong the magnetic field is.

The Earth's magnetic field is very weak, so your generator delivers very little power.

How weak? Have you ever seen these button-shaped neodymium-iron-boron magnets, also known as "neomagnets"? (Be careful – they can really pinch you).

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

They have magnetic fields that are about 6,000 times stronger than the Earth's magnetic field. Magnetic fields in electric generators are similar.

Even fridge magnets have magnetic fields that are about 200 times stronger than those of the earth.




Read more:
Curious Kids: Why do leaves fall from trees?


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