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Download Science One Physics Lecture 10 Circuits => Magnetism
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Transcript
Science One Physics Lecture 10 Circuits => Magnetism Clicker[Q] We close the switch. What is the voltage across the capacitor once the circuit has run for a while? (a) 0V, (b) 12V, (c) 40V, (d) 60V, (e) depends on the capacitance Clicker[Q] We close the switch. What is the voltage across the capacitor once the circuit has run for a while? (a) 0V, (b) 12V, (c) 40V , (d) 60V, (e) depends on the capacitance 1820: Electricity and magnetism are linked! Magnetic fields v e moving electron reacts to magnetic field at its location moving electron generates a magnetic field in all of space F e v Magnetic field and force moving charge q magnetic dipole m field force/energy µ0 q v × r̂ 4π r2 Biot-Savart law F = qv×B Lorentz force µ0 B= (3(mr̂)r̂ − m) 4πr3 magnetic field of dipole E = −mB B= Clicker[Q] Clicker[Q] Clicker[Q] Clicker[Q] [Q] [Q] [Q] How can we determine the strength and direction of a magnetic field? Strength and direction of a magnetic field [Q] How can we characterize the strength of a magnet? What is the magnetic counterpart to electric charge? Characterization of magnets How can we characterize the strength of a magnet? What is the magnetic counterpart to electric charge? • For magnets, orientation matters ⇒ Magnets are characterized by a vector-valued quantity, the magnetic dipole moment m. Clicker[Q] Clicker[Q] Magnetic field and force moving charge q magnetic dipole m field force/energy µ0 q v × r̂ 4π r2 Biot-Savart law F = qv×B Lorentz force µ0 B= (3(mr̂)r̂ − m) 4πr3 magnetic field of dipole E = −mB B= Clicker[Q] Clicker[Q] Field of a magnet m: strength & orientation of magnet (magnetic dipole moment) r: vector from center of magnet to probe location B= µ0 (mr̂)r̂ − m 4π r3 Along the axis of the magnet, m||r, µ0 2|m| |B| = . 4π r3 A magnet in a magnetic field m0: magnetic dipole moment of second magnet B: magnetic field The energy E of the second magnet in the field B is E = −m0B Biot-Savart law – B-field of a moving charge Biot-Savart law – B-field of a moving charge µ0 qv sin θ B= 4π r2 B = µ0 q v × r̂ 4π r2