1. Magnetism & Electric Currents CH 21.2

2. Electric Currents Produce Magnetic Fields A wire with a current flowing will create a magnetic field Metal filings placed around the wire will make a pattern showing the magnetic field

3. Right hand rule Used to find the direction of the magnetic field Point thumb in direction of current Curl your fingers inward This is the direction of the magnetic field

4. Hans Christian Orsted Danish Related magnetism and electricity

5. Hans Christian Oersted First to demonstrate effects of current on a compass Magnetic field of the current carrying wire exerts a force on a compass needle –Weak force Needle turns in the direction of the wire’s magnetic field –Needle points tangent to the direction of the current

7. Solenoid Increasing the current increases the force –High current is dangerous Wrapping the wire into a coil also increases the force Solenoid is an insulated wire coiled –Each loop adds to the magnetic field next to it –Result = strong magnetic field –Develops north and south poles like a bar magnet

10. Increasing Solenoid Strength 1. More loops adds strength  loops =  magnetic field 2. Increase the current 3. Placing a rod of material with magnetic properties –Result is an electromagnet –Rod becomes a magnet, which adds to field

11. Electromagnetic Devices Galvanometers – detect current (movement of charges) Magnetic field of coiled wire interacts with field of magnet inside –Force turns the core –Core turns needle

12. DC Motors Coil in motor keeps spinning as current moves though –Coil is flat Coil can do work if attached to a shaft or propeller Commutator alternates the direction of the current every half turn

14. DC Motor Brushes connect wires to the commutator Current changes direction every time the brushes come in contact with a different side of the ring

15. Speakers Convert an electrical signal to a sound wave –coiled wire, permanent magnet, cone Coiled wire around a paper cone –Current in wire creates field that interacts with the field of the magnet Paper cone vibrates with alternating current –Sound waves from vibrating cone

17. Other Devices Hair dryers telephones cassette/VHS tapes