Along, hollow, cylindrical conductor (inner radius = 2.0 mm, outer radius = 4.0 mm) carries a current of 12 a distributed uniformly across its cross section. a long wire which is coaxial with the cylinder carries an equal current in the same direction. what is the magnitude of the magnetic field 3.0 mm from the axis?

Explanation:

As we know that by ampere's law we have

here we know that enclosed current here at radius r = 3 mm is given as

now from above equation we have

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