69.  The wire in Figure 21.37 carries a current of 12 A. Suppose that a second long, straight wire is placed right next to this wire. The current in the second wire is 28 A. Use Ampère’s law to find the magnitude of the magnetic field at a distance of r = 0.72 m from the wires when the currents are (a) in the same direction and (b) in opposite directions.

 

afg040

Figure 21.37

 

Ampere’s Law is

 

Using this to find B for a long straight wire produces

 

 

 

When currents are in the same direction

 

 

When currents are in the opposite directions

 

 

This will result in the magnetic field going in the opposite direction as part (a)

 

 

 

 

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This page last updated on June 21, 2018