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Magnetism Chapter 36 What is a Magnet? Material or object that produces a magnetic field. Two types: Permanent Electromagnet What causes Magnetism? In order to create a magnetic field, a charged particle must be moving. Moving and spinning electrons cause magnetic fields in every object. Domains A small region of space where the magnetic fields produced by moving electrons are aligned together. Often, the directions of the domains cancel each other out. Ferromagnetic material Cancellations do not occur, resulting in a net magnetic field Domains Magnetism Opposites poles attract Like poles Repel Magnetic Poles can not be separated Every object that has a north pole has a south pole Magnetism Magnetic Field Region around a moving charged particle through which a force is exerted on another moving charged particle Similar to Electric Fields Magnetic Field Lines Lines are not real North South (outside magnet) Can not cross Closer lines mean stronger field Magnetic Field Lines Magnetic Field Lines Magnetic Field Magnetic Field is a region around a moving charged object through which a force is exerted on another moving charged particle Motion of particle must be perpendicular to the magnetic field Magnetic Fields Magnetic Fields are often illustrated using arrows Magnetic Fields What about into the page or out of the page? Into Page Out of Page Magnetic Hand Rules To determine the direction of the force, we use hand rules. Different hands for different charges Right hand for Positive charges Left hand for Negative charges Conventional Current Conventional Current follows the old “convention” that positive charges are the charges that are moving in current Use Right Hand Rule Electron Current Electron Current is the reality that negative charges are the charges that are moving in current Use Left Hand Rule Magnetic Hand Rules Point index finger in direction of motion Point palm or other fingers in direction of magnetic field Point thumb in direction of Magnetic Force Example An electron is moving through a magnetic field as shown below. In what direction will the magnetic force be? e Out of page Another Example An electron is moving through a magnetic field as shown below. In what direction will the magnetic force be? e Down Force on Wire Still use hand rule to determine the direction of the magnetic force Index finger is the direction of the current Magnetic Fields produced by Currents A current carrying wire also produces a magnetic field Direction follows second Hand Rule Magnetic Fields produced by Currents Second Hand Rule Thumb in direction of current Curl fingers around wire Curled fingers show direction of magnetic field Example What is the direction of the magnetic force exerted on wire 2 by the magnetic field produced by wire 1? I- 1 2 IDown Example What is the direction of the magnetic force exerted on wire 1 by the magnetic field produced by wire 2? I- 1 2 Down I- Magnetic Fields produced by current carrying loops Imagine current flowing through the loop below In what direction will the magnetic field be produced inside the loop? Into Page I- Electromagnets Temporary magnet caused by an induced magnetic field from current carrying wires. Electromagnets Current carrying wire produces a magnetic field Coiling the wire bunches up the magnetic field inside the coil Electromagnets Increasing the strength of the electromagnet: Increase Current in wire Increase number of coils Add an iron core Electromagnetic Induction If charged particle moving through a magnetic field feels a force, shouldn’t a moving magnetic field exert a force on a charged particle? Electromagnetic Induction A voltage can be “induced” in a wire by moving a magnet near the wire. often a coil of wire is used Faraday’s Law Induced voltage is directly proportional to the number of coils, cross-sectional area of the coils, and rate of change of magnetic field Electromagnetic Induction Electromagnetic Induction Electromagnetic Induction Inducing a current in a coil of wire creates its own magnetic field Electromagnetic Induction Changing direction of magnetic field changes direction of induced voltage Creating an alternating current (AC) Alternating Current Current alternates direction at a regular rate Electrical Outlets Direct Current Current flows in one direction only Batteries Sim Generators & Motors Device to convert between Electrical and Mechanical Energy Generator Converts Mechanical Energy to Electrical Energy Motor Converts Electrical energy to Mechanical Energy Generator Motor