P.Sci.

1. P.Sci. Unit 6 cont. Ch. 21 Magnetism

2. Magnets • Permanent magnets – are magnetic all the time (lodestones) • Other substances can be made into permanent magnets by placing a strong permanent magnet near them or by stroking them with a permanent magnet.

3. Materials are classified as either magnetically hard or soft. Hard – easily magnetized but looses magnetic properties easily. Soft – difficult to magnetize but does not loose its magnetic properties.

4. Magnetic Force • the invisible force exerted by magnets. • It depends on: • the strength of the magnet • the distance an object is from the magnet

5. Magnetic Poles • Magnets have a pair of poles, a north pole and a south pole. • Like poles repel (S/S or N/N) • Unlike poles attract (N/S) Just like with electrical charges North Pole SouthPole

6. Magnetic Fields • The region where a magnetic force can be detected. • Magnetic Field lines are used to show the magnetic field. A compass needle will always point along a field line. The lines are close together where the magnetic force is strong, and spread out where it is weak

7. Earth as a Magnet • Earth acts like a giant bar magnet. It has a North and South pole. These magnetic poles are not the same as the geographic poles.The pole that is above Canada is actually a magnetic South pole and the one in Antarctica is a North pole – to reduce confusion they are named for the geographic pole

8. . Earth’s magnetic field has changed direction more than 20 times in the last 5 million years.

9. Magnetism and Electric Currents • In 1820, Hans Oersted found that magnetism is produced by moving electric charges by experimenting with the effects of an electric current on the needle of a compass.

10. A current-carrying wire creates a magnetic field that forms in concentric circles around the wire. Right Hand Rule – if you hold a wire in your right hand with your thumb pointing in the direction of the + current, your fingers would curl in the direction of the magnetic field.

11. The magnetic field created by the current-carrying wire is very weak. To create a stronger magnetic field: Increase the current in the wire Wrap the wire in a coil (solenoid)

12. Solenoids • Each loop of wire adds to the strength of the magnetic field of the loop next to it. • The strength of the magnetic field depends on the number of loops of wire and the amount of current in the wire.

13. Electromagnet • If you add an iron rod in the center of the coil (in a solenoid) it will create an electromagnet. This adds to the magnetism of the coil creating a stronger magnet. Electromagnet

14. Electromagnetic Devices • Galvanometers – used to measure current in ammeters and voltage in voltmeters. • Electric motors – convert electrical energy to mechanical energy to cause motion. • Stereo speakers – magnetic forces cause motion that produce sound waves

15. Faraday’s Law • An electric current can be produced in a circuit by a changing magnetic field. • Electromagnetic induction -moving a magnet in and out of a coil of wire causes charges in the wire to move.

16. Electric Generator • converts mechanical energy to electric energy by electromagnetic induction

17. Alternating Current (AC) • For each ½ rotation of the wire loop, the current produced by the generator reverses direction or alternate. See table on page 477

18. Electricity in Your Home • The electricity you use in your home is created by large generators at the power plants. • The mechanical energy used to power the generators can come from: Running water (dams), burning coal, nuclear fission, wind, hot water (geothermal)

19. The electricity coming from a power plant is too strong for you to use in your home.

20. Transformers • increase or decrease the voltage so that it can be used. • Step up – increases voltage primary coil < secondary coil • Step down – decreases voltage primary coil > secondary coil