Magnetism

1. Magnetism Bill Nye & the first 2 right-hand rules

2. Review: What elements are magnetic? • Unlike electricity, NOT all metals can be magnetic: • Of the about 100 elements we know about, ONLY iron, nickel, and cobalt can become magnetic (whereas almost all metals are good electrical conductors). • Note aluminum can NOT become magnetic. Don’t be confused by references to Alnico magnets made of aluminum, nickel, and cobalt. Aluminum is only a filler in those magnets!

3. Review: HOW do iron, nickel, & cobalt become magnetic? …. • The “electron-spin” of electrons in atoms is called the “domain”. In all of the elements, the electron-spins are going every which way, and essentially canceling each other out. (See figure a at right.) • In iron, nickel, and cobalt, the electron-spins or domains can become aligned. (See figure b at right.) • When the electron-spins/domains of iron, nickel, or cobalt become aligned, then they become magnetic. • Note – you can NOT say just “electrons” become aligned. It is either “electron-spins” or “domains”. Be very careful about that! • Remember - NOBODY really understands what’s going on! Why do those three elements electron-spins do that? Why only those three? Find out yourself, and get a Nobel prize in Physics!

4. Review: Magnetic Domains aligned & not… “stroking” technique; what’s the other? How could you get domains unaligned? By dropping or heating the magnet!

5. 2 kinds of charge: + and – Can have single charges alone Opposite charges attract Like charges repel Neutrals are ALWAYS attracted through “induction” Electric fields do exist, field lines do not; closer field lines more powerful/forceful there; field lines around +-, --, and ++ you already know 2 kinds of poles: N and S Can NOT have single poles alone (no “monopoles”; if you break a magnet in half, you just get 2 smaller magnets that both have N&S poles.) Opposite poles attract Like poles repel ****“Neutrals” (meaning in this case samples of iron, nickel, & cobalt that are NOT yet magnetized, or do NOT yet have their electron-spins/domains aligned) are ALWAYS attracted. Magnetic fields do exist, field lines do not; closer field lines more powerful/forceful there; field lines around a single bar magnet are closed loops from N to S; other combo’s look similar to electricity, as if N=+ Electricity vs Magnetism

6. Electricity & Magnetism are “wed”: • *Electricity causes magnetism.... • There are 2ways to make iron, nickel or cobalt domains aligned: • “stroke” a needle/nail over & over again in the same direction with a magnet (see bottom left of slide 4) • but also by wrapping a needle/nail with a wire (several coils all going in the same direction) and attach the wire to a power supply like a battery (an “electromagnet”) • Cst 5f=“Students know magnetic materials AND electric currents (moving electric charges) are sources of magnetic fields and are subject to forces arising from the magnetic fields of other sources.” • “All magnetic fields are actually caused by the motion of _____ particles inside the metal. A spinning electron constitutes a “charged particle in _____.”

7. More on electricity causes magnetism: • Compasses laid out around a current-carrying wire will point in the direction of the magnetic field, which happens to form a circle around the wire. Forms concentric circles with magnetic field tangential to circle at all points

8. Electricity & Magnetism are “wed” • *Magnetism causes electricity.... • Watch us spin the handle to cause a lightbulb to light (but only if the magnet is attached!) • This is an example of a generator. • 5h=“Students know changing magnetic fieldsproduce electric fields, thereby inducing currents in nearby conductors.”

9. Quick Review: • Generators are a device that converts _____ energy into _____ energy. • Batteries are devices that convert _____ energy into _____ energy. • Motors are a device that converts _____ energy into _____ energy. • Transistors are made up of semi-conductors; 1 T = amplifier in a circuit, many T = fast switch in a circuit

10. Temporary vs permanent magnets: • Do the domains remain aligned for a long time after you remove the thing that was doing the aligning? (ie: remove the current, and/or remove the other magnet) • If YES – its a “permanent” magnet • If NO – its only a “temporary” magnet • In the picture, the needle/nail hanging from the magnet is only a temporary magnet, as it will lose its magnetism once it is removed from the bar magnet.