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Transcript
Do Now (2/5/14) Do not touch the materials on your desk until instructed to do so. 1) Are all metals magnetic? 2) Can non-magnetic materials interact with magnets? Intro to Electromagnetism Copper Tube Demo • You will have 10 minutes to complete the Demo Activity. • Do not drop the magnets on the floor! • Please ignore air resistance in your answers. Copper Tube • What did you observe when you dropped your pencil? • What did you observe when you dropped the magnet? • Was the magnet attracted to the copper tube? • What guesses did you come up with for why this occurs? Electric Current and Magnetism • • In 1820, it was hypothesized that the electric current must produce a magnetic field around the wire. Michael Faraday wondered if the reverse might be true!?! Energy Transfer He discovered that he could induce current by moving a wire through a magnetic field What type of energy transfer is this? Kinetic Energy to Electrical Energy Inducing a Current • It is the relative motion between the wire and the magnetic field that produces a current. What if the wire moved parallel to the Magnetic Field? Would current be produced? NO CURRENT IS PRODUCED IF THE WIRE MOVES PARALLEL TO THE MAGNETIC FIELD Current • What sort of shape do magnetic field lines form around a current carrying wire? Exit Question: A wire of length 10 cm moves parallel along a magnetic field of strength 8T such that none of the field intersects the wire. If the wire is moving 500 m/min what is the resulting current through the wire? Do Now (2/6/14) 1. What must be true for a current to be induced in a wire as the wire moves through a magnetic field? 2. A uniform magnetic field B, with magnitude B = 1.2 x 10-3 T, points vertically upward throughout an enclosed space. A proton with a velocity v = 3.2 x 107 m/s enters the space moving horizontally from south to north. • Find (a) the magnitude and (b) the direction of magnetic field. Lets Change Gears What is the name of a force acting on an object that moves in a circular path? What is the direction of centripetal force? Towards the center of the circle Mass Spectrometer • Mass Spectrometer o Measures the mass of an unknown atoms or molecules RHR • Why does the particle curve downwards? Radius of the Circle Name the two forces in the diagram Magnetic force == centripetal force Lets solve for the radius of the circle: mv qB r mv r qB Identify our Variables • • m = Mass v = Velocity • • • r = Radius q = Charge B = Magnetic Field Strength Apply RHR Is this particle an electron or proton? Proton How do we know if this particle is an electron or proton? RHR Moving through a Voltage • V = voltage • v = velocity • Q = Charge • M = Mass v 2qV m Classwork Use the rest of class time to work on your homework. ‘Interaction between E and B and matter’ Do Now (2/7/14) • An electron moves at 4.2 x 105 m/s as it passes through a magnetic field. What is the radius of it’s circular path? Electricity • What are different ways we generate electricity? • Hydro-electric Dams • Wind Power • Generators • Solar Power • Fossil Fuels What type of energy transfer is this? Kinetic Energy to Electrical Energy EMF What occurs if a wire moves through a magnetic field? A current is induced • • A force is exerted on the charges in the wire. This increases the electric potential energy on the charges. EMF • What have we learned before that uses the word ‘potential’? Potential Difference! (ΔV) This change in potential, or potential difference is called the induced electromotive force, or EMF. EMF • Electromotive Force (emf) - IS NOT A FORCE o It was defined before we fully understood electricity. o Think of it as a voltage. • The EMF (ε) is measured in volts and depends on: ε=Blv Where l is the length of the wire. Classwork Use the rest of class time to work on your homework. Either: ‘Interaction between E and B and matter’ Or ‘Electromagnetic Induction’ Cool videos Feel free to watch these on your own time http://www.youtube.com/watch?v=txmKr69jGBk magnet: http://www.youtube.com/watch?v=FM3LVrKXFcA