L19_Viet_Biot-Savart and Ampere¦s Laws

L19_Viet_Biot-Savart and Ampere¦s...

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Unformatted text preview: Physics 122 Electricity and Magnetism Lecture 19 Biot-Savart and Amperes Laws 05/07/09 Physics 122 - Lecture 19 2 Magnetic Force A current consists of moving charges. Amperes experiment implies that a magnetic field exerts a force on a moving charge. This is true, although the exact form of the force relation was not discovered until later in the 19 th century. The force depends on the relative directions of the magnetic field and the velocity of the moving charge, and is perpendicular to both.. ( 29 F q v B = r r 05/07/09 Physics 122 - Lecture 19 3 The Hall Effect When a charged particle moves in a vacuum, it experiences a force that is perpendicular to its velocity in a magnetic field. In 1879, Edwin Hall, a graduate student at Johns Hopkins Univ., discovered that the same behavior is true of charged particles moving in a conductor. Edwin Herbert Hall (1855 1938) H m d e V F ev B F eE e w = = = = H d V wv B = / d J I A I v ne ne wtne = = = H I IB V wB wtne tne = = The sign of the mobile charges matters !!! 05/07/09 Physics 122 - Lecture 19 4 Example : Hall Probe Measurement of Magnetic Field A Hall probe consists of a strip of metallic bismuth that is 0.15 mm thick and 5.0 mm wide. Bismuth is a poor conductor with a charge carrier density of n = 1.35x10 25 m-3 . The Hall voltage on the probe is measured to be 2.5 mV when the current is 1.5 A. What is the magnetic field, and what is the electric field inside the bismuth? 4 25-3 19 (1.5 10 m)(1.35 10 m )(1.6 10 C) (0.0025 V) (1.5 A) 0.54 T H tne B V I-- = = = (0.0025 V) 0.50 V/m (0.005 m) H V E w = = = 05/07/09 Physics 122 - Lecture 19 5 The Cross Product Form of the Biot-Savart Law ( 29 2 4...
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L19_Viet_Biot-Savart and Ampere¦s...

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