Answer to Question 3

 

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A current of 2.0 A flows through a coil that has 150 turns.  The coil is made on a former of  square section 2.0 cm 2.0 cm, and 10 cm long.  In the coil there is a material of relative permeability 150.  Calculate the reluctance.

First work out the flux density:

B = (4p 10-7 H m-1 150 150 2.0 A) 0.10 m = 0.5655 T

 

Now work out flux:

F = 0.5655 T (4.0 10-4 m2) = 2.262 10-4 Wb

 

Now work out the reluctance:

 

S = (150 2.0 A) 2.262 10-4 Wb  = 1.3 106 H-1