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Unformatted text preview: Y ? (c) The gap between plates X and Y is then filled completely with a material of resistivity η , so that a current I flows from Y to X with a uniform current density. Draw an equivalent RC circuit for the system, and hence find the initial current and the time for the current to drop to 1 − e of the initial value (Neglect dielectric effect). Fig. 1 3. A nonconducting circular disc of radius R has a total charge +q uniformly distributed over its surface. The disc rotates about its axis at a constant angular velocity ω . Starting from BiotSavart law, derive an expression for the magnetic field produced by the disc along its axis. In particular, what is the magnetic field at the centre of the disc? [ Hint : ( ) z z R z R dr z r r R 2 2 2 2 2 2 2 3 2 2 3 − + + = + ∫ ]...
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This note was uploaded on 10/14/2010 for the course PHYS 2051 taught by Professor Drkwong during the Spring '10 term at CUHK.
 Spring '10
 DrKwong
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