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Module 4, Lecture 7: Introduction to Magnetism Magnetic Field and Force • Magnetic north and south poles’ behavior is similar to electric charges. A moving charge or an electric current produces an electric field and a ________ _________ in the surrounding space. • The magnetic field exerts a ______ on any other moving charge or current that is in the field. • • For magnets, like poles _____ and opposite poles _______. • A permanent magnet will attract an un-magnetized metal (like iron) with either the ________ or _________ pole. B • In contrast to electric charges, magnetic poles always come in _________ and cannot be isolated. – Magnetic field F q (v B ) B Breaking a magnet in two yields two magnets, not two isolated poles. Force F is ____________ to both v and B units of _________ T 1 T = 1x104 G (Gauss) 1 T = N /(A·m) EF 152 Lecture 4-7 1 Examples 3̂ 5̂ 6 m/s. 0 qv rˆ B 4 r 2 1 c2 A beam of protons (q =1.6 x 10-19 C) moves at 3.0 x 105 m/s through a uniform magnetic field of 2.0 T. The velocity of each proton lies in the xz-plane at an angle of 30° to the +z-axis. Find the force on a proton. Lecture 4-7 2 A moving charge will generate a magnetic field relative to the velocity of the charge. 4 ̂ mT What is the magnetic force on the particle? EF 152 Lecture 4-7 The Magnetic Field due to a Moving Charge A particle with charge q = –2 µC has a velocity of 7 ̂ The magnetic field is: EF 152 0 0 0 10 7 T m / A 4 3 EF 152 Lecture 4-7 4 Magnetic field - straight current-carrying wire B Field around two wires carrying current in opposite directions 0 I 2 r Btot A long, straight 120 V wire powers a 1500 W hair dryer. At what distance is the magnetic field from the conductor equal to the earth’s magnetic field in Knoxville, about 0.51x10-4 T? EF 152 Lecture 4-7 0 I r 2 R 2 B 0 I 2r xd d d x Two wires carry 12.5 A in the opposite direction and are 3 mm apart. At what distance is the magnetic field from the conductor equal to the earth’s magnetic field in Knoxville, about 0.51x10-4 T? 5 rR x 2 d 2 2d = distance between wires x = distance from midpoint Field of a long cylindrical conductor B 0 Id EF 152 Lecture 4-7 6 Simple DC Motor rR R = radius of cylindrical conductor Magnetic field outside cylindrical conductor is same as for a straight wire EF 152 Lecture 4-7 7 EF 152 Lecture 4-7 8