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# hw7 - Electricity and Magnetism I(P331 Homework 7 Due...

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Electricity and Magnetism I (P331) Homework 7 Due: Wednesday, November 4, 4:00 PM 1. A Hall probe is a device for measuring magnetic fields. In a typical device a current I flows in a ribbon of n -type doped semiconductor located in the magnetic field. In an n -type doped semiconductor the charge carriers are electrons. In the steady state there is a voltage difference V H between the edges of the ribbon, such that the net perpendicular force on a charge carrier q E + q ( v × B ) is zero. From V H one can determine B . (a) Assume the geometry shown below. The material is As-doped Si, with 2 × 10 15 conduction electrons per cm 3 , and resistivity 1.6 Ω · cm. (You may need to hunt down the formula for computing resistance from resistivity .) The current is driven by a 3 V battery across the 1.0 cm length. What Hall voltage will be measured across the 0.2 cm width if the field strength is 0.1 T? (b) Show that the sign of V H depends on the sign of the charge carriers. Edwin Hall measured V H in metals in 1879 and found that the charge carriers are negative.

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hw7 - Electricity and Magnetism I(P331 Homework 7 Due...

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