Lect_15_note

Lect_15_note - Chapter 29 - 3 Magnetic Fields FB on a...

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Chapter 29 - 3 Magnetic Fields
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B Magnetic Field ± Lorenz force F = q E + q v x B
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Moving Charges in a Conductor F = q E + q v x B - - - - - - - + + + + + + + E F E V H
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Moving Charges in a Conductor F = q E + q v x B + + + + + + + - - - - - - - E F E V H
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Hall Effect
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Hall Effect Edwin Hall discovered this effect in 1879, while working on his doctoral thesis . American physicist 1855 to 1938
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Hall Voltage - - - - + + + + E H ± The charges accumulation establish an E field which apply a force on the moving charges against the magnetic force. ± The charge accumulation stops until F B =F E . Then charges move straightly. ± F = q E + q v x B So, E H =v d F E
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Hall Effect - - - - + + + + E H ± While charges accumulate at the two sides, a potential difference is generated in a direction perpendicular to both the current and the magnetic field ± V H = E H d F E V H
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Hall Voltage - - - - + + + + E H F E ± When E H =v d B ± The potential difference between the up and the bottom edges V H = E H d = v d B d ± I = Δ Q / Δ t = nqv d A = nqv d td ± v d d = I / ( nqt ) H H I I BRB V nqt t ∆= =
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Hall Voltage R H = 1 / nq is called the Hall coefficient H H II BRB V nqt t ∆= =
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Application of Hall Effect ± The Hall effect gives information regarding the sign of the charge carriers and their density R H = 1 / nq ± It can also be used to measure magnetic fields B = V H t / (R H Ι )
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This note was uploaded on 01/28/2011 for the course PHYS 011 taught by Professor Nianlin during the Fall '08 term at HKUST.

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Lect_15_note - Chapter 29 - 3 Magnetic Fields FB on a...

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