A hollow cylinder with an inner radius of 4.0 mm and an outer ...

[KWilfred]

A hollow cylinder with an inner radius of 4.0 mm and an outer radius of 30 mm conducts a 3.0-A current flowing parallel to the axis of the cylinder. If the current density is uniform throughout the wire,
 
  what is the magnitude of the magnetic field at a point 12 mm from its center? (0 = 4  10-7 T  m/A)
  A) 7.2  10-6 T
  B) 8.0  10-6 T
  C) 8.9  10-7 T
  D) 7.1  10-8 T

Question 2

A long, straight wire with 3.0 A current flowing through it produces magnetic field strength 1.0 T at its surface. If the wire has a radius R,
 
  where within the wire is the field strength equal to 36 of the field strength at the surface of the wire? Assume that the current density is uniform throughout the wire. (0 = 4  10-7 T  m/A)
  A) 0.36 R
  B) 0.060 R
  C) 0.64 R
  D) 0.030 R

[bitingbit]

Answer to Question 1

A

Answer to Question 2

A

[KWilfred]

Excellent

[olderstudent]

Thanks for the timely response, appreciate it