GCSE PHYSICS - MAGNETISM AND ELECTROMAG - LESSON 5 - magnetic materials iron and steel
Comparison of Magnetic Properties: Iron vs. Steel
Understanding Crystal Grains
- Both iron and steel consist of crystal grains, which are the fundamental structural units in metals.
- Under a microscope, iron's larger crystal grains can be observed, with boundaries where different grains meet known as grain boundaries.
Differences in Grain Size
- Steel has smaller crystal grains compared to pure iron (wrought iron), making it harder and less malleable.
- The presence of carbon (up to 4%) in steel contributes to the smaller grain size, resulting in more grain boundaries than in iron.
Magnetic Domains and Their Behavior
- Magnetic domains within both materials point randomly when not magnetized; these domains represent magnetic fields produced by the crystal grains.
- When an external magnetic field is applied, larger crystal grains in iron allow for easier realignment of magnetic domains compared to steel's smaller grains.
Magnetization and Demagnetization
- Iron's larger crystal grains facilitate easier magnetization but also make it easier to demagnetize once the external field is removed.
- In contrast, steel retains its magnetism longer after being magnetized due to its smaller grain structure.
Experimental Demonstration of Magnetic Properties
- A simple experiment using a permanent magnet shows that chains of iron tacks collapse when removed from the magnetic field, indicating easy demagnetization.
- Conversely, chains of steel paper clips remain intact after removal from the magnetic field, demonstrating their ability to retain magnetism.
Classification of Materials Based on Magnetism
- Iron is classified as "magnetically soft," meaning it can be easily magnetized and demagnetized.
Understanding Magnetic Materials and Their Applications
Permanent Magnets vs. Electromagnets
- The goal of creating permanent magnets is to ensure they retain their magnetism after the external magnetic field is removed. This requires using magnetically hard materials.
- While steel can retain its magnetism, other materials like ferrite, neodymium, and alnico are superior for this purpose due to their enhanced magnetic retention capabilities.
Characteristics of Magnetically Soft Materials
- Magnetically soft materials are advantageous for specific applications such as electromagnets and transformer cores. These materials allow for quick magnetization and demagnetization.
- In an electromagnet, when the switch is activated, current flows through a solenoid that magnetizes the core material. It’s crucial that this core material can easily demagnetize when the switch is turned off.
Core Material Requirements
- The ideal core material for both electromagnets and transformers is pure iron (or soft iron), which allows rapid changes in magnetism without retaining it.