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What we’ll need for today… • • • • • Magnets (bar and horseshoe) Iron filings Compasses Two wires, 4 batteries in series, light bulb Electromagnets (solenoids) James Clerk Maxwell Michael Faraday Electromagnetism Magnets: What do you know? Magnets – Key Points • Have poles (N and S) rather than + and – for charges • Like poles repel; Opposite poles attract • Produce a magnetic field: B similar to gravitational field: g and electric field: E • Magnetic Flux refers to the density of field lines The Tabletop Explainer… Magnetic Field (B) • • • • Vector quantity (arrows) Points in direction a compass would point Runs from North to South Allows for FM: Magnetic Forces (the reason a compass needle moves!) Where does the electro come in? • Current carrying wire…. Current carrying wire… • A static distribution of charges produces an electric field • Charges in motion (an electrical current) produce a magnetic field 1st RHR A moving electric charge produces a magnetic field • Thumb: Direction of Current • Fingers: Curl in direction of magnetic field What happens then….. If we have a whole bunch of current carrying wire wrapped tightly? Electromagnets Arranging wire in a coil and running a current through produces a magnetic field that looks a lot like a bar magnet Solenoid (electromagnet) The 2nd RHR: Fingers: Direction of current through solenoid Thumb: Points to north pole Cross section: Magnetic fields inside a solenoid B = µo I n B: Magnetic Field Strenth (Tesla T) µo : Permeability of free space = 4π x 10-7 T·m/A I: Current (Amperes A) n: Loops per meter = N/l N: total loops l: length Example A hollow solenoid is 25 cm long and has 1000 loops. If the solenoid has a diameter of 4.0 cm and a current of 9.0 A what is the magnetic field in the solenoid? 3rd RHR Applies to: 1.Charges moving in a magnetic field 2.A current carrying wire in a magnetic field Cross Product Cross product: Vector product of two vectors. Gives a new vector that is orthogonal (perpendicular) to both 3rd RHR Direction: Thumb: current/particle motion Fingers: Magnetic Field direction Force: Palm (positive); Knuckle (negative) Mass spectrometer 3rd RHR For a charge moving in a magnetic field, a magnetic force is applied to it. FM = q v x B (cross product) For us… FM = qvBsinθ q: charge v: velocity B: Magnetic Field strength θ: orientation Example A proton is fired into a magnetic field as follows: Find/show: a) It’s path b) FM c) Radius of it’s path 3rd RHR For a current carrying conductor, the magnetic force is as follows: FM = B I l sin θ If the conductor is perpendicular to the magnetic field: FM = BIl B: Magnetic Field strength (T) I: Current (A) l: length of conductor (m) θ: orientation 3rd RHR For a current carrying wire in a magnetic field, a magnetic force is applied to it. FM = B I L sinθ B: Magnetic Field strength I: current L: Length of wire in magnetic field θ: orientation