Chapter 30197P30.26(a)BNIrinnerTmAAmT==×⋅×=−µπ07324109001401020700360ejaf...(b)BNIrouterAmT×=−02210900140130194...*P30.27We assume the current is vertically upward.(a)Consider a circle of radius rslightly less than R. It encloses no current so fromBs⋅=zdI0insideBrbg=we conclude that the magnetic field is zero .(b)Now let the rbe barely larger than R. Ampere’s law becomes BRI20πµ=,soBIR=02.FIG. P30.27(a)The field’s direction is tangent to the wall of the cylinder in a counterclockwise sense .(c)Consider a strip of the wall of width dxand length A. Its width is so smallcompared to 2Rthat the field at its location would be essentiallyunchanged if the current in the strip were turned off.The current it carries is IIdxRs=2up.The force on it isFBup=×=FHGIKJ×=IIdxRIRIdxRsAAA224002intopageradiallyinward.FIG. P30.27(c)The pressure on the strip and everywhere on the cylinder isPFAxRdxIR=0202242AAinward .The pinch effect makes an effective demonstration when an aluminum can crushes itself as
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This note was uploaded on 12/14/2011 for the course PHY 203 taught by Professor Staff during the Fall '11 term at Indiana State University .