Ch12 - magnetism notes
- 1. Magnetism 2000 years ago, rocks in Magnesia, Greece were found to have weird properties. Later called “lodestones.” Hans Christian Oersted (Danish Science Professor, 1820) Discovered relationship between electricity and magnetism accidentally while demonstrating electric currents. These caused a compass needle to tip.
- 2. Similarities to Electricity • Exert non-contact force – Has a Field • Strength of force depends on distance • Attract and Repel ∴ there are 2 parts (north & south) – Opposites attract -- Like pole repel Differences from Electricity • You can get 1 e by itself. You can never get a North pole without a South Pole and vice versa. S NS N S N S N
- 3. Magnets & Electricity • Electrons & magnetic fields – Remember electron spin? • Charge in motion causes a small magnetic field. – Many electrons spinning in same direction produces … • Magnetic Domains – Clusters of aligned electrons spinning in the same direction – How is a weak magnet different from a strong magnet? • Stronger magnets have more aligned domains
- 4. Magnetic Domains How strong are these magnets? Why?
- 5. Magnetic Field (B) Area around a magnet that affects other magnetic objects. Measured in Teslas (T) Vector or Scalar? N S Rules for drawing Leaves Object perpendicular Out of North into South more lines stronger field Field is strongest at the poles Magnetic Force caused by Magnetic Field F = q v B – qelectron & proton = 1.6 x 10-19 C
- 6. 1st Right Hand Rule Direction of the magnetic force is perpendicular to the velocity and the field 1st Right Hand Rule (3 Dimensions) Tells you the direction of the force. • Place your fingers in the direction of B • your thumb in the direction of v • palm tells direction of the force • out of + into – Since this deals with 3 Dimensions… mean going into the page (feathers of an arrow) mean coming out of the page (arrowhead)
- 7. • Find the direction of the force for each of the following on a proton. v B B Bout Bin v v v
- 8. More Right Hand Rule Practice • Find the B Field in the following: F F V V V XXXXXX XXXXXX F XXXXXX XXXXXX