If a circular conductor carries a current of ‘I’ ampere having radius ‘r’ meter, then the magnetizing force at the center of the coil is given by

• A. (1/r)*(At/Wb)
• B. (1/4r)*(At/m)
• C. (1/r)*(At/m)
• D. (1/2r)*(At/m)

Answer: (D)

Magnetic Field Strength (H)  gives the quantitative measure of strongness or weakness of the magnetic field.
H = B/μo
Where
B = Magnetic Flux Density
μo = Vacuum Permeability
The magnetic Field strength at the center of circular loop carrying current I is given by
B = μoI/2r
B/μo = I/2r
H = I/2r At/m
Where r = Radius