# How Special Relativity Makes Magnets Work | Summary and Q&A

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September 23, 2013
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Veritasium
How Special Relativity Makes Magnets Work

## TL;DR

Electric and magnetic fields are intertwined due to the effects of special relativity, explaining the functioning of electromagnets and permanent magnets.

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### Q: How does passing an electric current through a metal convert it into an electromagnet?

When an electric current passes through a metal, the density of positive and negative charges in the metal changes. This change in charge density generates a magnetic field, resulting in the metal becoming an electromagnet.

### Q: What role does special relativity play in electromagnets?

Special relativity explains the phenomenon of length contraction, wherein moving objects appear contracted in their direction of motion. This contraction leads to changes in charge density, enabling the creation of a magnetic field in an electromagnet.

### Q: Can electromagnets work without the effects of special relativity?

No, the functioning of electromagnets relies on the principles of special relativity, particularly the phenomenon of length contraction. Without these effects, there would be no changes in charge density and no generation of a magnetic field.

### Q: How do permanent magnets differ from electromagnets?

Permanent magnets do not require the flow of electric currents, as they possess inherent magnetic properties. The alignment of magnetic domains within the material, specifically magnetite, is responsible for the magnetism exhibited by permanent magnets.

## Summary & Key Takeaways

• Electromagnets are created by passing an electric current through a metal, causing changes in the density of positive and negative charges, leading to the generation of a magnetic field.

• Special relativity, which states that length and time are perceived differently by observers in motion, plays a role in the functioning of electromagnets.

• Permanent magnets, on the other hand, are not reliant on electric currents and are explained by the properties of magnetite and the alignment of magnetic domains.