Enercon Sample Problems

Sample Problem no. 1

Sample Problem 9

A solenoid has 250 turns. What is the magnetomotive force when the current is 0.12A?

A small 60 Hz single-phase transformer has 10.2 watts at no load. The core has a volume of 750 cubic cm. The maximum flux density is 10,000 gauss and the hysteresis constant of the core is 5 x 10−4. Using the Steinmetz law to find the hysteresis, determine the eddy current loss.

Sample Problem No. 2 How many magnetic lines of force will pass a 5 sq. cm. perpendicular area on a magnetic field having a flux density of 2000 gauss? Sample Problem 3: If a current of 5 A flows through a long wire of radius 0.004 meter, what is the m agnetic field intensity produced 0.02 meter away from the surface of the wire. Sample Problem 4: A certain laminated steel core has a permeability of 3000. The length is 5 cm and the t he cross section is 2 sq cm. What is the reluctance? Sample Problem 5: A magnetic coil is made up of 500 turns wound around a magnetic circuit of 1.5 x 10−2 reluctance. A current of 0.25 ampere flows through the coil. What is the flux through the magnetic circuit? Ans = 10,471.975 maxwells Sample Problem 6: A solenoid has a magnetic reluctance of 2.2 x 10−. It has 300 turns and a core area of 5 sq cm. What is the flux density when the current flowing is one (1) ampere. Ans = 34,271.92 gauss Sample Problem 7: The relative permeability of a certain silicon steel is 4500. A certain magnetic loop consist of a silicon steel of 10 cm square, 20 cm long and an air gap of ¼ cm. What is the reluctance of the magnetic circuit? Ans: ℜ = 2.544 x 10−2(cgs units)

Ans: = 4.55 watts Sample Problem 10: The pole face of a magnet in a telephone receiver has dimensions of 12 mm x 2mm. If the flux between each pole and the diaphragm is 4 , with what force is the diaphragm attracted to the poles? Ans: F = 0.266N Sample Problem 11: A conductor 0.5 m in length and c arrying a current of 10 A is placed in a magnetic field whose flux density is 20 0 Wb/2 . If the plane of the conductor is inclined at an angle 30 deg from the plane of the magnetic field, what is the force exerted on the conductor? Ans: F = 500 N Sample Problem 12: A pair of straight parallel bus bars of c ircular cross section is spaced 20 cm apart. If each bar carries a current of 50,000 A, determine the force in newton per meter which the conductors have to withstand. Ans: F = 2500 N/m Sample Problem 13: Calculate the flux, flux density, and field intensity on the magnetic structure in figure. Given:  =1,000, N = 500 turns, i=0.1 A,  =0.1m, h=0.1m w=0.01m

Sample Problem 8: A magnetic circuit consists of silicon steel o f 3000 permeability, of 10 cm length and a cross section of 1.5 sq cm and an air gap of the same cross section and of 2 cm length. A ½-ampere current flows through the 5000-turn coil. What is the field intensity at the air gap? Ans: H = 1568.24 oersted

Find: ∅, ,  wb/sq m

 : ∅=1.76 x 10−5 ,  =0.175

Sample Problem 14: The magnetic circuit shown has dimensions   =  = 9 2 , g = 0.05 cm,  =30 cm, and N = 500 turns,  = 70,000 for core material (a) Find the reluctance ℜ  and ℜ . For the condition that the magnetic circuit is operating w ith  =1.0 T, (b) Find he flux ∅ and (c) the current 

  = 