And Electricity! Chapter 8 Section 2

 1820: Hans Ørsted happened to have compass close to a wire with current flowing  The compass needle deflected away from magnetic north when the current was turned on and returned when the current was turned off  Hypothesis: magnetic field radiates in all directions from a wire carrying an electric current

 Based on Ørsted’s work we know electricity and magnetism are related  Any moving charge produces a magnetic field Direction of magnetic field around wire depends on direction of current

 If we loop a wire around a metal center, we amplify the magnetic field created by the current  Electromagnet is a temporary magnet created in this way

 If we reverse the current, the poles of the electromagnet are reversed  Electromagnets can be turned on or off by turning the current on or off

 Electromagnets are used in many devices:  Speaker: ▪ Has a permanent magnet attached to a cone ▪ Has an electromagnet ▪ When electromagnet changes poles, it is attracted or repelled by the permanent magnet ▪ Movement of the cone makes sound ▪ HowStuffWorks "How Speakers Work" HowStuffWorks "How Speakers Work"

 Galvanometer  Galvanometer has a fixed magnet and a coil of wire making an electromagnet  When current goes through electromagnet it is attracted or repelled by fixed magnet so it moves  Needle attached to moving coil measures amount of current ▪ Voltmeter ▪ Ammeter

 Electric motor  Electromagnet that can rotate between poles of permanent magnet  Current through electromagnet makes it attracted and repelled to poles of permanent magnet  HowStuffWorks "How does a brushless electric motor work?“ HowStuffWorks "How does a brushless electric motor work?“  YouTube - Direct Current Electric Motor YouTube - Direct Current Electric Motor

 Read pages  Answer questions 1-6 on page 239: due 12/2/09