Chapter 8

1. Chapter 8 Magnetism & Its Uses

2. Sec 1: Magnetism • Over 2000 years ago Greeks first discovered magnetism in a mineral they called magnetic. • Magnetism—properties and interactions with magnets • Magnets attract metal objects.

3. Magnetic Force &Magnetic Fields • Magnetic force—the interaction between magnets. • The strength of this force increases as magnets move closer together. • Magnetic field—the area surrounding a magnet that exerts the magnetic force. • Iron and other magnets react to the magnetic force when placed in the magnetic field. • Magnetic field can be represented by lines of force, or magnetic field lines.

4. Magnetic field lines of a bar magnet

5. Magnetic Poles • Magnetic field lines are closest to each other at the ends of the bar magnet • These are magnetic poles—where the magnetic force exerted by the magnet is the strongest. • All magnets have a north and south pole. • Bar magnet—poles are at opposite ends • Horseshoe magnet—the poles are the two ends (like a bent bar magnet)

6. Interacting Magnets • Magnets either attract or repel each other. • When 2 north poles or 2 south poles come close, you can feel a force preventing the magnets from touching. • North poles always attract south poles. • When 2 magnets come close, their magnetic fields combine.

8. A Compass Needle • A compass contains a needle (a small bar magnet) that is free to rotate. • When placed near a bar magnet, the north pole of the needle will turn towards the south pole of the magnet. • A compass needle will point towards the North Pole of Earth. • Earth acts as like a gigantic bar magnet, and its magnetic field extends into space.

9. Earth’s Magnetic Poles • The north pole of a magnet is the end of the magnet that points towards geographic north. • The north pole of a magnet attracts a south magnetic pole. • Earth’s south magnetic pole is near the geographic north pole. • It is located in Canada about 1500km from the geographic north pole.

10. Magnetic Materials • A magnet will not attract all metal objects. • Only a few elements can be made into permanent magnets • Iron, cobalt, & nickel • Objects made from these metals are not always magnetic. • Put an iron nail next to a refrigerator, let go, and it falls to the floor. • You can make these metals behave like magnets temporarily.

11. Permanent Magnets • Iron, cobalt, or nickel can be made into permanent magnets by placing them in a strong magnetic field. • This creates a magnetic field inside the material • It can retain magnetic properties for a long time. • Permanent magnets can lose their magnetism if heated or dropped. • When a magnet is broken, each piece still has a north and south pole! • Even the smallest pieces of a magnet have a north and south pole.

13. Sec 2: Electricity & Magnetism • Electric currents cause magnetic fields. • The magnetic field around a current-carrying wire forms a circular pattern around the wire. • The strength of the field depends on the amount of current flowing in the wire.

14. Electromagnets • Electromagnet—a temporary magnet made by placing a piece of iron inside a current-carrying coil of wire. • When current flows through the loop of wire, magnetic field lines form around the wire. • The more loops of wire, the stronger the magnetic field.

15. Properties of Electromagnets • Electromagnets are temporary because they are only magnetic when current is flowing through the wire. • Electromagnets convert electrical energy into mechanical energy to do work.

16. Stereo Speakers • The mechanical energy produced from an electromagnet vibrates parts of a speaker to produce sound.

17. Electric Motors • Electric motor—a device that changes electrical energy into mechanical energy. • Contains an electromagnet that is free to rotate between poles of a permanent magnet connected to the battery. • When current flows through the electromagnet, a magnetic field is produced in the coil.