Download Lecture Slides Physics on Electricity + Magnetism = Induction and more Study notes Physics in PDF only on Docsity! 1 (Ch. 25) PH 104 w/ dr. g Lec 29 Electricity + Magnetism = INDUCTION !! How to get electric current from a magnet: Move a magnet in and out of a conducting coil! (demo) Voltage (electric field) is induced.= electromagnetic induction Must have relative motion between coil and magnet. Need magnetic field to thread through a conducting loop. Current induced is higher when R of wire is smaller Basically a magnetic force on an electric current: Magnet “sees”: charges in conductor moving with conductor Free charges get a magnetic force: get pushed along coil! How to get electric current from a magnet: Requires mechanical work “Inductance”: induced current opposes motion of magnet Induced current’s magnetic field is in opposite direction as magnet More loops = more induced fields opposite the magnet’s field Moving the magnet more difficult with: Larger loops and/or more loops Higher resistance in loops How to get electric current from a magnet: Faraday’s Law of Induction: Induced voltage ~ (number of loops) x (rate of change of the magnetic field within the loops) So: more induced voltage when: move the magnet faster have more loops use a stronger magnet Amount of current: depends on resistance. Direction of induced voltage: If positive while field in loops increasing (putting IN), then voltage is negative while field in loops decreasing (taking OUT) Where AC comes from: spinning coil in a magnet! Magnet in & out of coil: induced voltage changes sign: If positive while field in loops increasing (putting IN), then voltage is negative while field in loops decreasing (taking OUT) Voltage is alternating : corresponding current = AC ! Where AC comes from: spinning coil in a magnet! Another way: generator: turning conducting loop in field: Turning: area presented to field: oscillates So amount of field threading to loop also oscillates, Induced voltage is oscillating : corresponding current = AC. COIL = more loops => higher amplitude for induced voltage! Demo…
