20_InstSolManual_PDF_Part25 - Magnetic Field and Magnetic...

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20.86. Set Up: The magnetic field of a long straight wire is given by The magnetic field at the center of a circular loop is Let 1 refer to the wire and let 2 refer to the loop. The center of the loop is a distance from the wire. By the right-hand rule, at the center of the loop the magnetic field due to the wire is directed into the page and the magnetic field due to the loop is directed out of the page. Solve: Since and are in opposite directions, is larger than so the net field is in the direction of out of the page. 20.87. Set Up: The direction of the current is shown in Figure 20.87. The direction of is given by the right-hand rule. Figure 20.87 Solve: (a) Below the line the magnetic field is toward the east. (b) The field due to the current is the same order of magnitude as the earth’s field so is a problem. 20.88. Set Up: Calculate the magnetic field of the wire at the location of the electron. Then calculate the force this field exerts on the electron. The electron has negative charge so the force on it is opposite to the right-hand rule

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