Question

An MRI (magnetic resonance imaging) solenoid produces a magnetic field of 1.7 T . The solenoid is 2.5m long, 1.0 m in diameter, and wound with insulated wires 2.0 mm in diameter.Find the current that flows in the solenoid. (Your answer should be rather large. A typical MRI solenoid uses niobium-titanium wire kept at liquid helium temperatures, where it is superconducting.)

Answer 1

The number of turns wound is, 2.5m 2.0x10-'m =1250 The expression for the magnetic field inside the solenoid is, B=H.nl Here, I is the current in the solenoid, n is the number of turns per unit length of the solenoid, and He is the permeability of free space. The expression for number of turns per unit length is, N n = Here, N is the number of turns, and l is the length of the solenoid.

Combine n=- , and B = unl. B=w() I = B1 HN (1.7T)(2.5m) (47x10-> Tim (1250) = 2705.71A A