Basic Principles of Electromagnetism

C h a p t e r 4 | 99Absolute permeability,= µ µµ0r−7= (4π× 10 )(4000)= 5.027 x 10 -3 H/mREFERENCERobertson, C.R (2008) “Fundamental Electrical and Electronic Principles 3 rdNewnes, New YorkEdition”,PROBLEMS1. Find the magnetic field strength applied to a magnetic circuit of mean length 50 cmwhen a coil of 400 turns is applied to it carrying a current of 1.2 A.(960AT/m)2. A current of 2.5A when flowing through a coil produces an mmf of 675 At. Calculatethe number of turns on the coil(270 turns)3. A magnetizing force 8000 A/m is applied to a circular magnetic circuit of meandiameter 30 cm by passing a current through a coil wound on the circuit. If the coil isuniformly wound around the circuit and has 750 turns, find the current in the coil.(10.05 A)4. The maximum working flux density of a lifting electromagnet is 1.8 T and the effectivearea of a pole face is circular in cross-section. If the total magnetic flux produced is 353mWb, determine the radius of the pole.(0.196m)5. A coil of 300 turns is wound uniformly on a ring of non-magnetic material. The ringhas a mean circumference of 40 cm and a uniform cross-sectional area of 4cm 2 . If thecurrent in the coil is 5 A, calculate (a) the magnetic field strength, (b) the flux densityand (c) the total magnetic flux in the ring.(3750AT/m, 4.712mT, 1.885µWb)6. At what velocity must a conductor 75mm long cut a magnetic flux of density 0.6T if ane.mf. of 9V is to be included in it? Assume the conductor, the field and the direction ofmotion are mutually perpendicular.(200m/s)7. A conductor of length 15cm is moved at 750mm/s at right-angles to a uniform fluxdensity of 1.2 T. Determine the emf induced in the conductor.(0.135V)Basic Principles of Electromagnetism